Audemars Piguet

I would love some confirmation about the Ref. 26300 specifically. I hope there is someone here who can confirm a few details...

1) I believe that the main difference between the first-generation Ref. 25860 and second-generation Ref. 26300 is that the latter adopted the three-part "unibody" case (removable back) of the Offshore rather than the two-part case (fixed back) system of the original Royal Oak. Can you confirm that this is indeed the "case"? Did the stem/pusher tubes change at this point as well?

2) Most Ref. 26300 watches have the single deployant in the shape of the "AP" initials, but I see this on some earlier watches as well. And I've seen used Ref. 26300 watches advertised with the old rectangle deployant as well. Is this a signature of the second generation? Of course some older Ref. 25860 models also have the AP logo deployant, so it's quite confusing. When was this adopted? The City of Sails Ref. 25979 in particular seems to have the AP clasp even though it's a first-generation watch.

3) The most obvious visual distinction are the markers at 3, 6, and 9. These seem to be round on the original Ref. 25860 and rectangular on the Ref. 26300. But again I see some mix and match among used examples. Is this truly a distinguishing feature?

4) I've also heard that the bracelet is different but don't have any details on this...

Thank you so much for your help!