The Crusader's introduction date isn't a typo as far as I know. The 3R is actually a downgrade of the more advanced Crusaders used by the SLDF, and it looks like it was originally made for the mercenary and periphery market.
This happens sometimes. Usually because a product comes out before details about units have been fully ironed out, or a detail that since got changed (probably to iron out inconsistencies). Example: the War of 3039 historical lists the Mauler on the combine random allocation tables, but it has since been stated that the maulers fielded were actually the less sophisticated Daboku, which didn't exist when the war of 3039 book was published.
You might post a question in the ask the writers forum, but I think the standard answer is that the RATs are more guidelines than rules, and you should feel free to switch things out if you feel you need to.