[DavidKok]

I've been writing up my thoughts (none of which are original) for using 1NT as a Gazzilli bid over an unbalanced 1♦ opening. In this I've run into a small disadvantage - where the Gazzilli approach has a problem sequence that standard bidders would not have. I'm not sure if this can be fixed without changing the structure more than I'm comfortable with, or even if it should be fixed in the first place! So I thought I'd post it here, any and all feedback is very welcome.

The 1♦ opening shows an unbalanced (has a singleton or void) or semibalanced (5422, 6322, 7222) hand with primary diamonds and is wide-ranging in strength (from about 9 points to about 24). Additionally my partner and I like to open 1♦ on 'trumpy' 5332-hands with 5 diamonds, but we treat those as 6322 throughout so they are not an issue for system design. In particular, 1♦ shows 5+ unless 4=4=4=1 (we open 1♣ or 1NT with 1=4=4=4 and 4=1=4=4). Because of the wide range partner is expected to stretch with a major suit or diamond support. Suppose partner responds 1♠, showing 4+ spades, at least ~4 points or so and forcing. Over 1♦-1♠ I propose:
1NT - 6(+)♦ 10-15, or any 16+ (Gazzilli)
2♣ - 4(+)♣, 10-15, NF.
2♦ - 2-♠, 4♥, 5(+)♦, 10-15 NF.
2♥ - 3♠, 5(+)♦, 10-15, F.
2♠ - 4♠, minimum (so around 10-13), NF.
2NT - 4(+)♠, extras (around 13-15), F.
3♣ - 5(+)♣, 10-15, NF.
3♦ - 7(+)♦, broken suit, 10-15 NF.
3♥ - spade mini-splinter.
3♠ - not in use
3NT - Solid 7(+) diamond suit, at least AKQxxxx, 10-15 points.
4♣ and up are reserved for very shapely limited splinters (maybe voids exclusively?).

Over 1♦-1♠; 1NT* responder bids 2♣ with any 8+, letting opener describe their hand shape, and bids 2♦ or up with ~4-7 points. The response system I have patched together reads:
2♣ - any 8+
2♦ - ~4-7, 2(+)♦, (false) preference
2♥ - ~4-7, 4(+)♥, 5(+)♠, NF.
2♠ - ~4-7, 5(+)♠, NF. Shows 6 spades, or 5 with a club suit.
2NT - ~4-7, 4(5?)+♣, 3(+)♦, unbalanced, opener can show preference.
3♣ - ~4-7, 5(+)♣, NF.
3♦ - ~4-7, 4(+)♦, NF.
3♥ - not in use
3♠ - 6-7, good 6(+)♠ (at least KQJxxx)

Now give opener a hand like ♠x, ♥AJT, ♦AKQxx, ♣QTxx and responder ♠KJTxx, ♥xx, ♦x, ♣Kxxxx. In a standard system the auction would go 1♦-1♠; 2♣-3♣; 3NT, where responder can properly reevaluate their hand after learning of the club fit. In this Gazzilli-structure I might bid 1♦-1♠; 1NT*-2♠; ? and opener is stuck. The clubs are never announced, and 3NT seems out of reach facing a misfit and limited hand opposite. Alternatively it might be prudent for responder to get the clubs in, 1♦-1♠; 1NT*-3♣, which is winning here but costly if partner has something like a 2=3=6=2/2=2=6=3 when a partscore in spades is likely to be best. Systematically bypassing 5 spades to show 5 clubs also runs into issues if partner is strong - now I need to look for a 5-3 fit at the 3-level. Lastly responder can upgrade this nice 7-count to 8(+), but this runs into problems if partner was setting up to reverse into hearts.
Maybe this situation is rare enough that I should not waste my time on this - a sharp 3NT on a good 7 opposite a solid 16 thanks to the club fit. Or maybe there is a good and painless fix, in which case I'd love to hear it.

[nullve]

In my version of Gazzilli after 1♦-1M

1♦-1M; 1N-2♦

doesn't promise a single diamond, and Opener will always bid again on strong hands with only five.

[awm]

A few comments here:

1. I'd recommend not requiring 2♦ to promise doubleton. This helps you a lot with other hand types for responder (you can use 2NT+ to show various strong responder hands that help you a lot in sorting things out).
2. The problem you've described only really exists in clubs. You could probably use a 2NT bid (either direct or after 1NT..2♦) to show this precise hand type (1354 extras but not GF); you are not really worse placed than standard bidding for such hands.