Posted 2023-October-20, 14:24
This is one of the reasons that 2/1 has taken over with any pair that can both play it. I remember a "US vs Europe" invitational tournament (I think "Buffett Cup?") where everyone played with different partners on the team every session - so they had a "default card" people on each team would play with each other.
The US's was 2/1, Europe's was not - but there were exactly 5 auctions that were not GF. That lasted 2 days; and then they switched to 2/1 always GF. Because this is HARD to be precise on, harder than the 1NT forcing game, even for pros.
The way I was taught it (by JD, who will be well remembered by any long-time D18 player), in Standard (not specifically YC) a 2/1 promises a rebid unless opener bids 2NT or game. That's pretty easy to remember. It also means that as P_Marlowe says, 1♠-2♦; 3♦ shows extras and is GF; with diamond support and no extras, opener would bid 2NT.
As always, SAYC doesn't go into this in detail, because despite how it's been used since Matt Clegg posted it to OKB (1995 or so) it was designed as a system "all flight A" players in 1970 could play, not "system new players can learn"; so a lot of what's in there is "here are the standard decision points, and this is the choices we have made fore each." All the "so that implies <all this>" stuff is -- implied, because "all 1970 Flight A" players are assumed to know all that.
When I go to sea, don't fear for me, Fear For The Storm -- Birdie and the Swansong (tSCoSI)