ETA January 2014: This info has been reorganised over on Sutcliff Wiki:
http://sutcliff.wikia.com/wiki/Legions_and_Auxilia. Any future updates will probably occur over there.
While rereading I decided to track references to the various legions in the Roman British stories. Given her penchant for reusing facts and Sutcliffverse canon, if you will, I was curious which ones she used most often and what she said about them. ("Uh, maybe the ones stationed in Britain?" Well... yes, but.) This doesn't have any obvious use that I can think of, but perhaps you too are keen on useless information.
Obviously, you can read the actual history of these units elsewhere, but since I'm interested in what Sutcliff did with them, I've done no additional research (except dates, elsewhere) - the 'facts' here are what can be established purely from the texts and notes.
Listed by unit, rough date, text title, and note. Some references listed are merely repetitions of the same event, e.g. the loss of the Ninth Legion. The titles in quotation marks are short stories from The Capricorn Bracelet, except "Caratacus", which is a chapter from the not-really non-fiction Heroes and History. The protagonists of TCB are all named Lucius or Lucianus Calpurnius, so I've numbered them I-VI.
So - a brief history of the Legions according to Sutcliff:
Legio II Augusta - the capricorn badge; "Pia Fidelis"*
43 - "Caratacus" - Claudian conquest of Britain by Aulus Plautius; commanded by Vespasian
61 - Song for a Dark Queen - young Gn. Julius Agricola's legion
61 - "Death of a City" - joined by L. Calpurnius I
79-83 - Eagle's Egg - part of Agricolan campaigns in southwest and highland Caledonia
123 - "Rome Builds a Wall" - joined by L. Calpurnius I; part of Agricolan campaigns
126 - The Eagle of the Ninth - cohort of Gaulish auxiliaries commanded by centurion M. Flavius Aquila garrisons Isca Dumnoniorum (Fourth Gaulish, real unit, *see comments); apparently attached to 2nd Augusta?
150-ish - Outcast - first centurion Justinius builds the Rhee Wall of Romney Marsh; Cornelius Chlorus is legate
290s - The Silver Branch - centurion Marcelus Flavius Aquila and surgeon T. Lucius Justinianus posted to Magnis on the Wall
380s - "Caratacus" - Last legion to leave Britain
585 - Dawn Wind - Caerleon, II Augusta's headquarters, known as "the City of Legions"
Legio II Parthica - centaur badge
295 - The Silver Branch - once followed Carausius in Gaul; a vexillation lands in Britain under Asklepiodotus; Gaulish Cavalry?
Legio VI Victrix
123 - "Rome Builds a Wall" - L. Calpurnius II & 10th cohort detached for construction of Hadrian's Wall; Asturian auxiliaries
130 - The Eagle of the Ninth - stationed at Eburacum; Claudius Hieronimianus is camp prefect
130 - Swallows in the Spring - stationed at Eburacum; Wall construction rotation; Dacian Horse; Brigantes labour teams
150 - "Outpost Fortress" - stationed on the Wall; L. Calpurnius III in Dacian Horse
150s-ish - A Circlet of Oak Leaves - stationed at Trimontium w. Dacian, Asturian, Tungrian, Cretan auxiliaries; Aracos & Felix
343 - Frontier Wolf - stationed at Eburacum and sent to deal with Pict-Attacotti-Damnoni uprising
380s - Sword at Sunset - Maximus settled his veterans in Armorica; still inhabited in 470s - Bedwyr's home
Legio VII Claudia
295 - The Silver Branch - Lands in Britain with Constantius
Legio IX Hispana
43 - "Caratacus" - Claudian conquest of Britain by Aulus Plautius
61 - Song for a Dark Queen - destroyed by Boudicca
61 - "Death of a City" - stationed at Lindum; destroyed by Boudicca
80-83 - Eagle's Egg - Stationed at Eburacum; Agricolan campaigns in Caledonia, based at Inchtuthil; Quintus is standard-bearer;
117 - The Eagle of the Ninth - destroyed in Valentia; Marcus's father is first centurion; said to be cursed by Boudicca
123 - "Rome Builds a Wall" - destroyed in Valentia
130ish - Swallows in the Spring - Two survivors meet again in former HQ Eburacum under the Sixth Victrix
292-5 - The Silver Branch - putative connection to M. Flavius Aquila; eagle standard rediscovered in his house in Calleva and lost in Calleva basilica fire.
480s - Sword at Sunset - Damnonii's warhorses descended from cavalry mounts stolen from the lost legion
Legio X Fretensis ("Fretencis" (sic))
The Eagle of the Ninth - stationed in Judaea; Uncle Aquila commanded 1st cohort and Claudius Hieronimianus was tribune
291-2 - The Silver Branch - T. Lucius Justinianus stationed in Beersheba, Judea
Legio XIV Gemina
43 - "Caratacus" - Claudian conquest of Britain by Aulus Plautius
61 - Song for a Dark Queen - suppress druids under Suetonius Paulinus; defeat Boudicca
61 - "Death of a City" - suppress druids under Suetonius Paulinus; defeat Boudicca
83 - Eagle's Egg - with Agricola in SW Caledonia; redeployed to Germany
? - Dawn Wind - At some point, standard-bearer Marcus Petronius died aged 39 and was buried at Viroconium
Legio XX
43 - "Caratacus" - Claudian conquest of Britain by Aulus Plautius
61 - Song for a Dark Queen - suppress druids under Suetonius Paulinus; defeat Boudicca
61 - "Death of a City" - suppress druids under Suetonius Paulinus; defeat Boudicca
80 - Eagle's Egg - join IX at Corstopitum en route to Agricola
120s - Sword at Sunset - built the Hunnum (Onnum?) fort on Hadrian's Wall, with charging boar standard over the gate
343 - Frontier Wolf - stationed at Deva; sent to deal with Pict-Attacotti-Damnoni uprising
480s - Sword at Sunset - Artos uses their abandoned HQ at Deva "the City of Legions" as winter quarters
? - The Bridge-Builders - Androphon's father is a fort commander in north Wales
Legio XXX Ulpia Victrix
295 - The Silver Branch - land in Britain with Asklepiodotus; "a Lower Rhine Legion" that once followed Carausius
Frontier Scouts
180s - The Mark of the Horse Lord - stationed on the Northern (Antonine) Wall; Titus Hilarion captain
280 - "Frontier Scout" - L. Calpurnius V stationed at Credigone
343 - Frontier Wolf - Alexios Flavius Aquila & 3rd Ordo stationed at Castellum; 1st Attacotti recruited for deployment in Belgica; once received an influx of Syrian mounted archers
Dacian Horse (auxiliaries); invented by Rudyard Kipling in Puck of Pook's Hill
126ish - The Eagle of the Ninth - stationed at Isca Dumnoniorum under Lutorius
130ish - Swallows in the Spring - stationed at Trimontium "show off to their hearts' content" for visiting dignitary
150 - "Outpost Fortress" - L. Calpurnius III learns the fire ride as commander of 7th Troop at Trimontium
150s-ish - A Circlet of Oak Leaves - Stationed at Trimontium; led by Aracos, hold the cavalry line against Picts
196 - "Traprain Law" - Lucianus Calpurnius IV; suppress a Pictish incursion
295 - The Silver Branch - two squadrons desert the Portus Adurni garrison for Asklepiodotus's invasion force
Asturian Horse (auxiliaries)
123 - "Rome Builds a Wall" - Felix captains 30 auxiliaries attached to Victrix at Cilurnum
150s-ish - A Circlet of Oak Leaves - Stationed at Trimontium; stampeded by fire during battle with Picts
343 - Frontier Wolf - assist withdrawal from Valentia
Tungrian Horse (auxiliaries)
150s-ish - A Circlet of Oak Leaves - Stationed at Trimontium; stampeded by fire during battle with Picts
293 - The Silver Branch - Sylanus Varus, 5th cohort, 2nd Legion, stationed in Valentia 100-200 years earlier
The Navy
80-83 - Eagle's Egg - Agricola's troops build Theodosia station
150-ish - Outcast - Beric & Jason are rowers on the troop transport Alcestis of the Rhenus fleet
180s - The Mark of the Horse Lord - Theodosia garrisoned by Frontier Wolves but semi-decrepit
280 - "Frontier Scout" - Thetis, Thunderer, and Orion, stationed at Inveresk, destroy Sea Wolf envoy
290s - The Silver Branch - Carausius builds the Saxon Shore fleet and forts; Caleope stationed at Rutupiae
343 - Frontier Wolf - Inveresk station long-abandoned
Indeterminate / Miscellaneous
290s - The Silver Branch - Flavian and Justin's unit at Rutupiae. Probably the 2nd?
343 - Frontier Wolf - Alexios commands auxiliary cohort "3rd Britannica" at Abusina; Raetian auxiliaries
383 - "The Eagles Fly South" - L. Calpurnius VI's "3rd Spanish cohort"
450-ish - The Lantern Bearers - Aquila is a decurion of Rhenish cavalry
As always, additions, corrections, arguments, and "WTF"s are welcome.