First Printing of the Tactical Operations books still viable to use?
In Norway are not blessed with many gamestores that actually carry BT stuff. Since we are not in the customs union ordering from other countries can often increase the price by quite a lot since we have to pay VAT on shipping and charge for custom clearance.
See that one local store have the Tactical Operation Books (Advanced Rules and Advanced units and equipment) but the image on the store are the fourth (Rules) and first printing (units). I am going there this sunday to see for myself, but are first printings still usable. See that the current ones are sixt printing for both.
To answer my own post.
Found this handy guide on Goonhammer https://www.goonhammer.com/battletech-expanding-on-the-starter-boxes-books-and-inner-sphere/
And the Errata page on Catalyst. https://bg.battletech.com/errata/
Seems the split books are fourth printing of the original full volume for some confusing reason. They need to be used together and they are currently at 7th printing.
Judging by the erratas it's nothing major.
The original ORIGINAL books from the 80s are still fine to use. There have been only minor rules changes throughout, and there's errata available as you found.
Catalyst and Drive-thru-rpg also sell PDF versions of many of the books, if that's easier.