[caphm]

From my PS3, i've moved ASSENTION to "my favorites list" (may have the term wrong).
When i start the Netflix addon within Kodi on my Windows 10 HTPC, i can see it within "my favorites list" so i start watching it via Kodi.
However Assention is not subsequently shown within "current watch list" (again may have the term wrong).

As well, watching Start Trek series on the PS3 results in it being shown within "current watch list" but the episode watch status is not shown when i logg in vai the HTPC Netflix addon.
This goes the otehr way as well, so when watching an episode of Start Trek via HTPC netflix addon, it does not reflect as being watched via the PS3.

I thought that Netflix itself kept track of all the watched status, etc, via their servers, to allow their customers to roam across devices.

So is this an issue with the Kodi netflix addon or is this a misunderstanding on my part?

The add-on does not report watched state back to Netflix. It only pulls watched information from Netflix (one way). It's an often requested feature but unfortunately really hard to implement and we haven't (yet) figured out how.