Good point PN.
When I was on the UAS - effectively an Airman - the letter was a prefix. When I commissioned I kept the same number and the letter became a suffix.
I joined in the late 90s and as a former UAS student had a service number starting 2. I can't remember which way round it is, but graduate direct entrants and direct entrants straight from school at that time had numbers beginning with 8 or 5. FWIW, I think females' service numbers started with a 3.
So you should probably be looking for a service number starting 2, 5 or 8 and with a letter after the 7 numbers.