I think acl started in 35' I have a jumbo cola 1935 Owens Illinois bottle. I don't necessarily think this bottle is that old but it is the only one I have with the city on the acl in the back. If they are not OI bottles I really don't much trust the dating of those. I like it though a cool old Royal Crown. I have heard talk of acl process starting in 1934, but i have never saw proof in an acl bottle. Sodapopbob would know more on that subject than me.
In a SPBob thread from when there was a bit more ACL activity here, the oldest ACL to turn up was a 1934 Jumbo Cola barrel bottle. Next was 1935 7Up.
If you see a G1 on the lip of the RC Cola, I think the date code is on the opposite side.