So this is a fascinating issue - and I think we have to start with the history of the term "yacht rock" itself. While the musical sub-genre took place from the mid-70s to the early 80s - the term yacht rock didn't come about until the mid 2000s. It's hard to know its very original use, but the first documented use is in the series "Yacht Rock" (with Hollywood Steve) that some LA area film students produced and posted online. I posted episode 1 above and was familiar with it back then (2005 ish).
What this means is that the whole notion of yacht rock developed organically 25 or so years later based on what a bunch of songs from an era share stylistically. Yes, there's some genuine basis to attribute it to a sort of smooth, yuppy-ish, slightly jazzy sound to a boating vibe - but it's that specific sound and production value that defines yacht rock and not necessarily hard swim lanes about specific artists, or even dates.
Steely Dan, for example, definitely made some yacht rock. The Aja album has Deacon Blues, Black Cow, and Babylon Sister and are as yachty as rock gets. But most of the Steely Dan earlier catalog is not . . . not only because the timing isn't right but the sound/style isn't right. Aja came out in 1977, when the yacht rock sound was well underway, but there's probably examples of genuine yacht rock before that. Also, I think the genuine era was short, by about 1981, the real stuff was mostly over.
BUT all this means there's ample room for debate.