Mattdog,
I'm sure under FOI that the back copies will be available.
If you have snags PM me as some of the RN guys had snags with changes to flying pay during training back in the early 90's and they won with the threat of court action.
Basically there is a law (its old but a good un) that states if you were genuinely paid , ie you didn't have any concerns that you were being overpaid because you believed you were entitled to it and then spent the money in good faith - tough MOD, their checks and balances should be more robust and the responsibility lies with the administrator!
Additionally thay are not entitled to 'dock' the money from your pay until a case has been proven against you or you agree for it to happen.
Good luck - take 'em down with you!