blackshoe, on 2019-February-15, 10:14, said:
By definition, SAYC includes everything on the official card. If you're not playing some of those things, or you are playing something in addition to those things (there are, iirc, two or three exceptions having to do with card play) then you are not playing SAYC and should not call your system any kind of SAYC. In short, there is only one SAYC, and it's what's defined on the card and in the booklet.
Who made you the language ruler of the bridge world? Words mean what people use them to mean, not what some arbitrary piece of paper says.
The simple fact is that many people claim to play SAYC, even though they haven't studied the booklet. When I used to play with randoms on OKbrige, I had something like "SAYC -- remember, this includes Jacoby 2NT" in my profile, because I'd run into many people who had SAYC in their profile but didn't play this.
I think many of them simply think that SAYC is another name for SA; it's basically just 5-card majors, strong NT with simple Jacoby transfers, and regular Blackwood.
The SAYC booklet also leaves quite a bit unsaid, and you have to infer a number of treatments from the gaps. These inferences are not always completely obvious.