The last one’s OP statement is similar to his in that he has had his licence some 20+ years but does not have LGV/ PCV entitlement. There is one problem in that he has not informed DVLA of a change of address some 5 years ago.
The question is in which order would it best for him to proceed with his application:-
Apply for change of address to his present licence first and then apply for LGV entitlement or do the whole lot at once?
(What problems is he likely to encounter with DVLA after not informing them of change of address?)