Earlier AB-Is have both pickups wired in parallel. Those ABs have a special circuit called BluEQube that could be turned on/off with that switch. I'm not sure what it was supposed to be doing, but it's some EQ. Later ABs have the bridge pickup wired in series while the neck pup is wired in parallel - and it's a great thing. It made the BluEQube somewhat redundant and it was removed. No current models feature a BluEQube as far as I know.
Personally, I like both my pups in series mode individually. Combustions have the bridge pup in series stock, neck in parallel.
In case you don't know, pickups in series have more low mids and stronger output, while parallel pups are somewhat mid-scooped. So a series bridge pickup produces a nice mid-oriented sound that nicely complements the neck pickup, while producing equal output because there's less string movement near the bridge. Series/parallel modes don't change whether pickups are humbucking.
I can't help you with listing the differences between the two models, but I understand they're quite different beasts, i.e. owning them both might not be redundant.
Oh, and welcome to the forum!