User Guides in PDF format for each xx.x perpetual release

What problem do you see this solving?

Availability of a point in time user guide in pdf format that matches the perpetual release. For example when C1 v 16.2 is released with its feature updates, release a corresponding 16.2 C1 user guide in pdf format , then again months later when 16.3 is released etc etc. Alternatively flag new features and changes with release number beside them in the user guide. Otherwise someone on perpetual 16.2 has issues down the track when your help is at say 16.4 reconciling differences quickly.

When was the last time you were affected by this lack of functionality, or specific tool?

Since C1 23 was released. As far as I can tell, the issue exists that the online help matches the current release, but perpetual users will get confused as new features are added with xx.x releases.