How to identify Podcast progress?

How to tell if a Podcast has been played? (or partially played?)

I know that the device creates a .POS file so that it can resume a Podcast from it left off.
But does the device have an option to show which Podcasts actually have .POS files?

Similar to how iPhones etc do this (they put a circle next podcasts etc)

.POS file format?

Additionally: it seems to me that a .POS file which contains exclusively null bytes (i.e a 512kb chunk of zeros) means “This has been played until the end”; but is there a spec/API that can be used on a Linux machine (I am using ‘gPodder’ as my Pod catcher) to decode this file?