Technically both, but more so the former.

I had a heck of a time finding accurate docs on the correct apiVersion to use for things like my ingress and service files (they had a nasty habit of doing beta versions and changing config patterns w/ little backwards compatibility). This was a few years back when your options were a lot of Googling, SO, etc, so the info I found was mixed/spotty.

As a solo founder, I found what worked at the time and assumed (foolishly, in retrospect) that it would just continue to work as my needs were modest.

I assume the first one, but it's more complicated. K8s used to have a lot of features (included very important ones) in the "beta" namespace. There are no stability guarantees there, but everyone used them anyway. Over time they graduated to the "stable" namespace, and after some transitory period they were removed from the beta namespace. This broke old deployments, when admins ignored warnings for two or three major releases.