I can understand why you’re concerned…in our world of expiration dates it seems really odd to be letting something sit on a shelf for WAY past its “expiration date”. The big difference here is the bag…since the meat is stored in a cold (fridge), oxygen depleted environment (bag), the nasty bacteria that would normally spoil the meat can’t grow. Simple as that. The bag allows the moisture out but also keeps the oxygen out.
Wet aging is the same thing, except the bag doesn’t let the moisture out (wet aging is typically done in cryovac bags).
I’d suggest you get comfortable with the process and results, then start experimenting. Thats what I did 😉