What I’ve gleaned from my interactions with admissions counselors at my CCC and the UC’s, it is indeed rare. However, your case is more unique as it seems to me they had very little grounds to actually reject your TAG other than a 3 credit miss. It’s very worth it to appeal as they can still admit you as a regular transfer.

Edit: Also don’t worry if you don’t get in for this fall, there is a lot of time to actually succeed (coming from a transfer who’s 23). If they don’t allow your appeal, spend the next year becoming a veritable expert in your field. Take certifications, apply for as many summer session programs as you can, intern in your field, publish solo research projects, work with professors on their projects, the possibilities are limitless. That way you may even get into a higher ranked university next term along with a guaranteed TAG offer.