For those that have asked.
On the back of the PSP box by the barcodes, there will be either an ‘A’, ‘B’, or nothing at all located below “120V”. If you do not have a letter that means it was purchased sometime near the US release (meaning 1.50). Having the letter ‘A’ means that the firmware is a 1.50, and seeing a letter ‘B’ there means 1.51. Now you won’t have to open the box to know your firmware, and most people are willing to find you a PSP box with the letter ‘A’ or no letter at all.