Then how did he get promoted if he was a PFC when he took off? There's that other case of the guy in Iraq, Matt Maupin. He was a PFC when he was captured, was later killed by his captors, and a couple of years later when his remains were recovered the media was saying he was a Staff Sergeant. Does the Army just bump them up in grade on a regular basis on the assumption they'd have made that rank if they had served the whole period?
I wish I could answer your question. I was Army in the 60s. Promotions up to E-4 were pretty much automatic provided you weren’t a total screw-up. I had to go before the CO and a couple of Warrant Officers and answer questions to determine proficiency in my MOS in order to get my Spec. 5 promotion (that rank no longer exists, btw). Even then it was two more months before a slot opened up. While it’s possible to make SSGT. in one enlistment, it rarely happens. And regardless of when you are up for the promotion it’s not a gimme by any means.
Of course, that was almost fifty years ago. No doubt times have changed.