if I had to guess I'd say that state information is probably held on a per-client (Echo, your phone app, etc) basis
My experience with most apps is that the last read/listened to state is stored in the cloud for the account (at least for apps like Pocket Casts, TiVo, YouTube, etc.). This is what facilitates you watching/listening on one device, and then picking up where you left off from another.
Audible handles this differently with each progress state being stored at the device level, but allowing you to create bookmarks which
are distributed across devices via the cloud. Unfortunately, Alexa is not smart enough to access these bookmarks, at least when I try to get it to advance it simply goes to the next chapter.
This of course makes listening to podcasts and books a rather complex activity if you also tune in from another device before reaching the end of an episode or chapter. One way to simplify this might be to have Alexa record the last listening position on the card in the app when you pause or stop. This would at least allow you to manually resume the position on another device.
But going the other way would be impossible unless Alexa could access bookmarks in Audible, or implement skills for apps such as Pocket Casts. I have found no way to tell Alexa to start a podcast 20 minutes in, or to skip ahead any amount of time other than the next episode.