An additional 7 were in the can by the time the series premiered on September 28th.
Which would give them nine completed episodes when you factor in Farpoint
, plus "in the can" means completely done and ready for airing. I'm sure they probably had some that were shot and still waiting for post-production processing.
The ratings did continue to get better the longer the show ran, but it was an unqualified hit right out of the gate and never lost steam from a ratings perspective.
I was 16 when TNG first came out. I remember watching the first night.
TNG, in my mind, was a highly anticipated, uncertain experiment. There was tremendous doubt about whether or not it would work, if there could be Trek without Kirk-Spock-McCoy, and if there could be a "new" Enterprise.
I can't imagine it being an "unqualified hit right out of the gate" as you say. It became that, but early on, it was an unknown. Our look back is colored by all that has come since TNG first debuted; it may be hard to remember what it was like when all there was of Trek was TOS and the TOS movies.
STNG was a ratings success from episode one, it was increasing ratings in it's time slot 1100% over the previous year in some cases. It even beat network shows in certain areas.