When I joined in 1972 as an airman my Number like all others at the time started H8100, then when I was commissioned in 2002 the prefix letter moved to the end of the number. Before I retired in 2010 however the dreaded JPA had arrived and my number disappeared from the computer system. So when I joined the ATC as VR(T) in 2011 I was issued a completely different number with no letter, the strange thing was that if I substitute the 4 with the letter H and rearrange the other numbers I still have the same number.