the text appears to be rewritten from the PSA descriptions in Campaign Operations and the advanced rules stuff is likely included for completeness. the rulebook for the box set is a pretty slim (48 pages iirc?) so there probably isn't going to be much beyond the basest of base rules
Correct.
So, full disclosure, I was one of the two writers who did the MechWarrior Cards. (The other was Geoff "Doc" Swift, a regular BT contributor as well.) And the directive was that the cards should be usable at all levels of the game, to the maximum extent possible. Which makes sense--the last thing you want is someone who just picked up the Beginner Box to not be able to understand and play with absolutely everything in the box.
But that created some challenges in our selection of the SPAs, especially on the cards in the Beginner Box. Something like "Natural Grace" (CO, p. 78) is a great, flavorful ability. But it touches on a lot of rules that aren't in the very first product a new player would pick up. (To say nothing of the amount of text that ability comes with, that needs to be crammed onto a card.)
It took some finagling, and not everything is 100 percent compliant to the rules in one box or the other, but I think we got close.