[Mbodell]

And does it matter if it is 1♦-2♣ versus 1M-2♣?

I know standard playing 2/1 strong nt is 2nt shows 12-14 or 18-19 while 3nt shows 15-17. But if you'd open 1nt with 12-14 your ranges seems to be 15-17 and 18-19. Should 2nt just show 18-19 now and 3nt show 15-17 (kind of fast arrival/same as with strong nt except without the weaker option)? Or is there some other good split for 2nt versus 3nt?

[gordontd]

Unless you open 1NT on all balanced 12-14s with a five-card major, you also need a rebid for balanced 12-14s. If you don't need that, then it makes more sense for the 2NT rebid to be 15-17 & the 3NT rebid to be 18-20 (forcing to 4NT) than the other way around.

[helene_t]

Even if you open all 5M332 hands 1NT when in range, 1♦-2♣ is different since you have to cater to 4441 with 12-14 points. Frances has worked this out.

[1eyedjack]

It is pretty common for 1♦-2♣-2♦ not to promise a 5th ♦
It is also not unheard of, esp in a weak 1N system, for 1♠-2♣-2♠ not to promise a 6th ♠. Certainly there is room to cater for it.
I personally favour opening 1N with 5M332, but even without that I also prefer to play 1♥-2♣-2♠ as showing extras, so a 2♥ rebid necessarily (in that context) does not promise a 6th.
I usually play 2N rebid as 15+ limited only by failure to open 2N. I dislike rebidding 3N with a balanced hand.