If you have enjoyed my recent writings on Cuddles and Dimples, and trying to pinpoint the exact moment at which the two tyrannical toddlers were retconned from being next-door neighbours to twin brothers, I am sure you will find this, by the excellent regular commentator Zoomy, of interest: a look at a Dandy Comic Library starring a solo Cuddles which was published after the retcon happened but had clearly been written before then, and has a bit of difficulty writing around the absence of Dimples (as well as clearly featuring the set of parents who were eliminated from the strip when the retcon happened).
A few months before that Comic Library was published, there had already been a joint outing for Cuddles and Dimples in the same range, no. 145 "The Holiday Horrors"; they appear to still be neighbours and not siblings in this one, as Cuddles' father (one of the set of vanished adults) is visible on the cover. The fact that the solo Cuddles story, seemingly written even before the two strips were combined, was released a few months after that is a real curiosity, almost as if it was sitting on the shelf for a while.
I did have a look through my Dandy annuals, and can report that by the 1990 book the boys are very clearly siblings (one story is a day at the beach and the other is set on Christmas Day; there can be no doubt these were produced after the retcon happened).
The 1988 annual still features a solo Dimples; when it was published, the neighbours-to-brothers changeover was happening, but the long lead times the annuals had meant that at the time it was being put together the Dandy and Hoot merger would not yet have happened. The Dandy Book 1989, which I don't currently have in my collection, may have featured stories where they were still neighbours, but that would probably be the only other publication at odds with what was happening in the weekly strip.