Source: http://www.abfevents.com.au/
The standard responses to the Jacoby 2NT are as follows:
| 1M | 2NT | GF, 4+ M |
3 /3 /3oM |
11+, Shortages | |
| 3M | 15+, No shortage* | |
| 3NT | 13-15, No shortages* | |
| 4x | Good second 5 card suit* | |
| 4M | 11-13, No shortages | |
* The meanings of 3M, 3NT and 4x may vary from what one might think «normal Jacoby» is, but that is not the main point.
There are two major problems with this:
(1) After bidding a shortage (which then proceeds into cue bidding), no one is sure about opener’s strength as it could be from 11 HCP to 17 HCP.
(2) Opener’s 4M bid showing a minimum with no shortages destroys any possible slam investigation if responder has a good hand.
A much better improvement would be to use 3 over 2NT as «any minimum» and subsequently 3 over that asks for a shortage. This way you can differentiate opener’s strengths when they have a shortage, and over 3 «any min» responder can now bid game if they have no slam interest thereby preventing any information leakage to aid the opponent’s lead/defence.
| 1M | 2NT | GF, 4+ M | |
| 3 |
Any minimum (roughly 11-14) | ||
| 3 |
Shortage Ask | ||
| Answers | 3 |
Club (Low) Shortage | |
3 |
Diamond (Middle) Shortage | ||
| 3NT | Other Major (High) Shortage | ||
| 4x | Cuebid, No shortage | ||
| 3 |
15+, No shortage | ||
| 3 |
15+, Club (Low) Shortage | ||
| 3 |
15+, Diamond (Middle) Shortage | ||
| 3NT | 15+, Other Major (High) Shortage | ||
| 4x | Good 2nd Suit | ||
| 4M | Does (should) not exist | ||
Note that a direct or delayed 3/3/3NT bids show a shortage with different strength.