Found a 20" Zenith Digital System 3

[Whirled One]

Just the other day at a Goodwill store I stumbled on this rather interesting "modern" Zenith.
I don't see very many Digital System 3's as it is, and this is the first time I've ever seen one with a screen size smaller than 27". This must have been one darn pricey 20" color TV, that's for sure... It even has a wood cabinet, and the built-in speaker system is well above average for a TV of this size.
It's an SE2035H made in September 1988. Set appears to be in good working order, but I haven't fully checked it out yet. Interestingly, it looks like this set may have originally been a hotel TV, as it is marked with "RM 3204" in marker on a couple places on the back, but I'd think a Digital System 3 would have been a darn expensive set for hotel use (perhaps some sort of luxury suite or something..?)

Questions:
- Did Zenith make very many Digital System 3's in smaller sizes like this..? Seems kinda odd to see such a 'high-end' chassis on a 20" TV.
- The input menu includes a selection for S-Video, but the back panel doesn't have an S-Video jack. Was an S-Video connection available through a breakout box that connected to the RGB port or one of the other edge-card connectors on the back? (What are the pin-outs on those things anyway..? For that matter, Is the RGB input just TTL-level digital (like for CGA/EGA displays) or is it analog?)
- When was the Digital System 3 line introduced/discontinued..? It was introduced in 1985, wasn't it? Did they continue making them all they way until the Closed-Caption decoder requirement in 1993 (which was different from the 'world-standard' Teletext system decoder used in these sets), or did they discontinue the Digital line before then?