Incidently, I don't see any allusion to a timeline in Barnett's words, and he does tell us himself that the regiment was in Ireland.
Which in itself is interesting for obvious reasons. ie Unless he's a Scots Guards Enthusiast (extremely dubious!) how does he know...only likely answer...Mary told him, which comes close to proving at least part of his testimony. (I'm sure I heard or read that somewhere before, incidentally, and wouldn't want you to think I'm claiming it's an original thought!)