@op; have they actually served you with an Enforcement Notice?
I can't see what your concern is because if you have evidence that it is > 4 years old, you simply state that in an Appeal, and that is the end of the matter. If you have supplied the LPA with clear evidence that it is more than 4 years old (regardless of repairs/refurbishment), they would be liable for your costs in any appeal, because they would have acted unreasonably.
All this talk of frontages and principal elevations and whatnot is totally irrelevant.