tangent

I've played Carrot Club in a regular partnership before (1C = 11-13 balanced or 17+ any). Generally, the players who normally play super-aggressive interference after strong 1C (e.g. 1S promises any hand with 3+ card spades when NV) don't use them anymore. Brown-sticker style interferences (psycho-suction, or a convention where bid of a suit showing that suit or 3 suiter short in that suit) also gets dropped. Not a good idea using those when having a game on your side is still very lightly. In conclusion, interferences are slightly less common and are more constructive than destructive.

Generally, I find it easiest to play that XX is forcing to 2 of openers suit. It may make sense to play it forcing to 2NT too. Reversing into 2S would be helping the opponents. They are already in trouble.

I find that using a weak NT (including all 5M332 hands) improves the 2/1 system a lot. I feel that the weakest part of the 2/1 system is the prepared minor rebid after the forcing NT where 2C or 2D rebid can be as short as 3 (or even 2!). Playing a 12-15 1NT, your minor rebids after a forcing NT will definitely be natural 4 cards. You do lose the ability to rebid 2NT with 18-19 (it's now 16-17) after a 1S opening though. It is also necessary to play the 1S/1NT reversal after a 1H opening (1S response becomes the forcing 1NT with 1NT rebid showing 16-18 balanced, and 1NT response is forcing with 4+ spades). Because of the load on the 1NT opening (12-15 with possible 5 card majors), you will need a more advanced response structure over the 1NT opening, and I highly recommend Keri over 1NT (from Ron Klinger's Bid Better, Much Better Over Opening 1NT) Other inferences to draw are 1M-2m-2NT shows a strong hand. 1m opening is almost always sound (either strong balanced hand or 5 cards, with the exception of 4441 shaped hands)

I've always been wondering about the legality (under WBF) of the 1S bid showing an unbalanced hand without a 4 card major (I've played that before and have seen that being played). It's definitely not brown sticker since that doesn't apply to 1 level openings. It's not really listed under the definition of a yellow (HUM) system, but point #5 (section 2.2 http://www.bridge.gr/dept/systems/policy.htm ) mentions " By partnership agreement an opening bid at the one level shows either length in one specified suit or length in another." Now this 1S opening does say something like "6+ either minor or at least 5/4 in the minors" so I'm not sure whether that qualifies. Of course, we know that anyone who likes to use this 1S bid intends to use the 2C opening for some particular nastiness... B)

The upper range for the non-forcing 2/1 would be just below the minimum required for the forcing response under that system. For moscito which uses the step response as the forcing bid showing 12+ hcp, the upper range would be 11 hcp. For viking which uses 1NT (or 1H over 1D) as the forcing response usually with 12+, the upper range also happens to be 11hcp too.

Not mentioned here yet, but Finnish Club has an interesting way to deal with those pesky 4M5C hands. 2H = 4 Hs and 5+ Cs 2S = 4 Ss and 5+ Cs Finnish club still uses short (2+) 1D openings even with the possibly of 1M being 4 cards, to handle 3325 shaped hands (another pesky distribution for strong club systems). Personally I prefer to extend the 1NT range to something like 12-15 to cover balanced hands below 1C strength so that 1D opening will only be made in 4+ cards. This makes for a more 'natural' strong club system.