suprgrover

I don't see how this makes any sense. The reference to "as A allows" means that LHO has always had the opportunity to accept the first insufficient bid. And "as in 3" means that the second insufficient bid is treated like a correction to a double or redouble. I have always assumed that the point of 27B4 is to adjudicate the following: N: 1♠ E: 4♣ S: 2♠ W: Did you say 2♠? S: Yes. But I'm changing it to 3♠. W: Director! I wanted to accept 2♠. 27B4 gives, I think, West the chance to accept the 2♠ bid but not the 3♠ bid.

Except for the elections that the ACBL can make as a Regulating Authority under the Laws, there really ought to be no differences. Alas, there is at least one. Law 12C1e, for adjusted scores when a Regulating Authority opts not to allow weighted scores, reads as follows in the WBF version of the laws: The ACBL version of the Laws includes "had the irregularity not occurred" at the end of clause (ii). The irony here is the the ACBL is the main user of 12C1e and managed, despite four members on the Drafting Committee, to get a version with which it apparently does not agree. There are a few other differences that I know of, but they seem immaterial (chapter headings and some omissions from the Preface).

so what does that say about (1♣) - 2♣ when 1♣ is Polish club or something similar, or (1♦) - 2♦ when 1♦ is 2+, etc? The ACBL Tech files say to alert 2♣ over a 1♣ bid that could be short, or a Polish 1♣ bid only if the 2♣ bid shows clubs. (Similarly, 2♦ over a 1♦ call that could be short is alerted only if it shows diamonds.) The logic seems to be that these bids are natural often enough that it makes sense to treat them as natural for alerting purposes.