I, as tiny little shit, was only trained up to like 7-digit addition (with far fewer examples given I suspect) and I also generalize near perfectly to 100+ digits.
amusingly, I realized recently that I've utterly forgotten how to do long division and had to work it back out based on vague memories. now you have me wondering if I need to check addition and multiplication too... it's been... awhile... since I've had to do much beyond quick mental math in my head.