Just because something is standardized, doesn't mean it didn't exist prior. And 1987 is the year the cabling standard was introduced.
have S-video hook-up connectors on the back
Really? The signals may be available, but do you actually know what an S-Video connector looks like?The reason I asked is because the Commodore 64 has one.
Output to a composite video monitor or analog RGB monitor, in addition to the CoCo 1 and 2's TV output. This did much to improve the clarity of its output.
As far as I know svideo is nowhere to be found because of the Motorola 6847 video chip, which was paired with the mc1372p to get the video output, and the mc1372p could be configured as rf or composite output according the the circuit.