Another insufficient bid

1H - (1NT) - 1S
This was against me, playing director, and I allowed 2S to be substituted but this is wrong because ....

1H - 1S is an unlimited bid so assuming a decent hand, say 9 or 10+ points, would double 1NT then 2 of any suit is not unlimited and therefore not comparable.

.... or is it ?

• Don't forget that the "lowest sufficient bid that specifies the same denomination" is still allowed. If it satisfies that, it doesn't need to be comparable. 27D might still apply, though.

• edited May 2018

In terms of comparability, you're looking the wrong way round. It's OK for the insufficient bid to be unlimited and the correction bid to be limited, just not the other way around; what's important is that any hand which would have made the correction bid would also have made the corresponding insufficient bid in the absence of intervention. (Or to think about the principles behind it: the AI from the correction bid has to at least duplicate the UI from the insufficient bid; it's OK if it's more specific. However, if it were less specific, the insufficient bidder's partner would have more information than they should, so that situation requires rectification.)

What does 1, 2 mean in this system (without the intervening 1NT)? Presumably not the sort of hand that would respond 2 after an intervening 1NT, unless playing weak jump shifts. Are there any other ways that the system could show a weak (but sufficiently strong) hand with spades over a partner's 1?

I agree with Mitch, though, that the case of correcting an insufficient natural 1 to a sufficient natural 2 is allowable even if they aren't comparable; it's a special case within the Laws.

• edited May 2018

There are three ways that the 2S bid would not bar partner from bidding:
1) The 1S bid was unintended, a mechanical error. The player can correct up until his partner has made a call.
2) As Mitch posted, "making it good" is allowable under Law 27B1(a).
3) The 2S is a comparable call to an insufficient 1S. It is more tightly defined than a sequence of 1H-1S, thus a subset. This would fall under 27B1(b).

In cases (2) and (3), 27D might apply and also, other than in case (1), the next player to call has the option of accepting the insufficient 1S bid.