I've always felt that the convention charts have been based on "who" wants to play "what" and making it legal. As a result, there seems to be a lot of inconsistency on what makes the list and what doesn't.
The argument about 'familarity' is circular. Nothing, no matter how simple it is on paper, can become familar if one never gets a chance to play against it. But somehow, strange treatments have made the list.
Transfer preempts are some of the simplest bids to defend against, yet they are relegated to mid-chart. But a 3N opener showing EITHER minor (akin to a multi 2
♦) opening is GCC?
I'm glad that Overcall Structure (1N overcall and Roman jumps) is legal under the GCC. Someone did a nice job lobbying for that at one time, and I like to play it.
While I get a dark pleasure out of making a 1N overcall of 1
♠ on: x, Axxx, Axxx, Qxxx and watching the client getting a befuddled look on his face and the pro across the table silently cursing me, I still pre-alert my OS bids, even though I don't have to.
The most egregious is a 1N opening showing an unbalanced hand of 16+ HCP. It amazes me how the ROMEX bids received GCC approval. I'd love to know the history on this one and how it got approved. Yet for some reason opening with 1
♥ or 1
♠ as a strong artificial opening is disallowed.
Doubles aren't regulated! Yep, your RHO can open ANYTHING, and an immediate double can mean ANYTHING.

I know a couple of loonies from L.A. that play an immediate double of a one bid is: a) any hand of 15 or more HCP, or b ) a 3 level preempt.

Yes its legal!
I hate to sound paranoid, but it appears treatments make the list because an elite group wants them legal. OTOH, certain treatments aren't legal for the same reason.
Its time to pull this whole process out of the smoke-filled back rooms. I would suggest that:
1. All proposed treatments are published on the league's web-site along with the date when C and C is going to consider such a treatment;
2. Proponents and opponents can provide written testimony supporting their views;
3. Written minutes of the meetings are made public after the fact.
I think #3 may already be in place, but I'd personally like it more conspicuously posted at acbl.org.