Does Bloggs still have a logbook from back then, or the little booklet thing that cadets record their flights in? The number of it escapes me just now.
If not I wouldn't hold out much hope for HQAC providing much evidence.
A year or maybe two ago, I had a guy get in touch looking for proof of his MoD FSS hours, as he'd lost his logbook. He'd not had any luck with asking the RAF. As it happens, we were able to provide sufficient evidence from instructor's old logbooks and other sources with a bit of effort