I imagine it was worded this way so someone couldn't just be "escaping" for an unknown length of time and just disappear - removes the incentive to not return right away. Still, I'm not how anyone would be able to prove or disprove which day he escaped in the first place - not like his captors gave him a receipt - so the whole thing is pretty goofy.
http://myarmybenefits.us.army.mil/Home/Benefit_Library/Feder...
It'd fit well - they kept trying to escape, and it'd have been easy enough to have a plot where they talk the camp commander into giving them a "fake" receipt in return for a favour, only for them to actually escape (and of course get caught again).
It kind of seems like the whole story is silly now...
This is why Bowe Bergdahl is in a big pickle if he is found guilty: he will lose 5 years of pay and return to his original low rank (he is now a Sergeant, I think he was a Private 1st Cl or Specialist) as well as be discharged as something other than "honorable".
I rather thought Bergdahl was in a “big pickle” because the charges against him both carry long prison terms (one potentially a life sentence).
He would have been paid if he had not escaped.