Ah, forget transfers, how lovely.
So, their real agreement is "hearts, or diamonds (if he forgot again)". If that's a legal agreement for 2
♦ over 1NT in the EBU, then it must be Alerted. If it was Alerted, and explained correctly, do you double? 90% of the time it's hearts, and you don't really want to have partner take out 2
♥ on the 5-1 split into your effective 1 trick, do you? And how do you make a takeout double of hearts (yes, I know there are several reasonable answers, but I do think that East "isn't clear about the Law" ("if I had been told it was diamonds, I would have doubled." "well, you wouldn't have been told it was diamonds, you would have been told it was 'hearts, or diamonds if they're rebid'. Doubling now?").
So, take a poll. Don't tell them that 2
♦ showed diamonds - because it didn't, that's just what he had - say it showed hearts or diamonds by agreement, and see what people do. Now, don't rely solely on that poll, because they are the NOS after all, but it's not as easy as it looks when "it just shows diamonds".
I hate forget transfers, and I want to punish NS so that they will fail to forget in future (because that's the only way they will remember, is if they get a few bad scores. I know these types). So I like about 30% 3
♥-1, 50% 3
♦+1, 20% 4
♦=, and a warning that either:
- they never treat this sequence as "diamonds only" again, or
- they start Alerting 2♦ and explaining it as "hearts, or diamond runout", or
- they're going to start getting automatic PPs for misinformation if I'm ever called to the table about this again.
When I go to sea, don't fear for me, Fear For The Storm -- Birdie and the Swansong (tSCoSI)