Ok, well that solves that one then. Thanks for the info. I hadn't realised that Cable's watch can travel inter-dimensionally as well as through time. So he went to the same time but in another universe in a bid to join the Avengers (clearly before the world-shattering events triggered by Thanos)
In order to make any sense of Logan's death being a trigger point, we now have to accept it took place way before 2029, when the Logan film was originally set. X23 is clearly now much older (by 8 years, as she is now 19) when we meet her again so that suggests Logan's death was in the past by some years.
I think they should have thought about all this a bit more but, oh well, it is what it is and all that. It was all just a big way to undo Wolverine's death (in a sense) by bringing a new version of him into the Deadpool timeline.
I'm now wondering which Earth the Marvels end scene with Binary and Beast is in. Is that another X-universe or the same one Deadpool and the new Wolverine are now in?