Peter - several Qs all rolled into a few posts. Firstly it looks like you mean LL276375, which was first registered in 2006
LL193855 was first registered in 2001. Each were registered and mapped using different Ordnance Survey detail
From a purely registration perspective we register the general boundaries so the plans are not supposed to be definitive or precise re where the legal boundary lies - see
PG 40 Sup 5 and indeed each of the other supplements for guidance
Measurements on a plan are helpful but again not definitive as 90 years on there's no certainty as to how they measured things and where from for example. And as OS detail confirms things can and do change re specific physical features. So whilst land/property can interlock like a jigsaw piece on the ground/in reality it is very rare that they do on deed/OS plans and as a result may not always do so on title plans mapped at different times. The general boundaries rule covers that scenario.
Mistakes can be made both in deed plans, OS plans and title plans and I can see that the solicitor contacted us on the 15th June and that contact is with the processing team for consideration. A response should be issued shortly but I'll flag it with colleagues to see if they can escalate it and trigger a reply asap