akwoo, on 2019-November-26, 00:59, said:
I think most people these days play that X shows 3 hearts and any other non-heart call (including pass) denies 3 hearts.
Without 3 hearts, pass shows 12-14, usually balanced, 2N shows 18-19, usually balanced (but what else do you do with 3154?), always with a stopper.
The hands without a bid are:
1) Those with 4 spades, 5 diamonds, less than 3 hearts and 15-16; with 17 you can bid 2♠ - you might be forced to rebid 2♦ despite only 5 diamonds here.
2) Those with 18 balanced, not 3 hearts, and no stopper - probably a stretch to 3♣ is best.
On your two hands without a bid, on (1) you can pass. Partner won't let the bidding die with 9+ unless he has a pile of clubs, and in that case, you may well be better off defending 2C then playing a very thin NT game with no source of tricks. Bidding 2D is actually more likely to slow down the bidding than passing. Partner will pass 2D with a misfitting 9 or 10, and now you are not likely to be in a good spot at all.
On (2), I don't think bidding 3C is much of a stretch. What else can you do?