Doesn't seem fair, does it! I think you might have a case. Try it, what have you got to lose?
They do often shift the goalposts with almost no comeback from us, so I'd go for it. I've done it in other areas and, whilst I didn't win, I did feel better that some PMA gnome (Pensions wallah, in my case) had to work a little bit harder to work out why and provide me with a plausible (he didn't) answer. I copied my letter to my MP (former Chancellor of Exchequer) who actually responded before the pensions people did!
Way ahead. Speak to your NCO i/c Allowances; explain your rationale; and get him/her on board. Then write to the appropriate AFPAA or PMA desk at Innsworth (Allowances will advise) asking for an explanation as to why you are in the psotion that you now find yourself.
Nothing ventured, nothing gained!