You can't be faulted for trying. When I was in the service, my mail followed me. I may have gotten it a month after it was sent, but it always got to me eventually.
If you are using the last address you had, and no update was sent, you can only be judged as having met your side of the obligation. That said, use caution as you proceed to the next steps in your collection efforts. That is, I would do more with "locators" within the military before I would jump into any court action.
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AndyZ CRCM
My opinions are not necessarily my employers.
R+R-R=R+R
Rules and Regs minus Relationships equals Resentment and Rebellion. John Maxwell