Its not that hard... regimental baggage overrun, assumed all is lost, but the guy had it in his backpack.... I even have a group where a MAN was reported lost and killed, memorial service by his family, etc. etc... and was announced as a POW a month later... with tens of millions of people involved and millions or personal dramas... there is plenty of opportunity for something to be reported lost, but then found again.
A personal example... when I was in the army we left Central africa in emergeny to go to zaire... the guys on base had to pack the material we left behind. Stuff was thrown away or went missing... through no fault of our own... all had to be replaced...