ToffeeDan

Great answer - I apologise for the original confusion in describing the situation.. YOU have understood every bit of it and provided a comprehensive reply and an understanding - yes, I see how 2S should be alerted as the systemic meaning. Yes, to the opener it must be natural and yes, I as opener did have 5161 hand. Thanks, and I will upload my hand when I know how to do these things, except that it was more an exercise in understanding what to do when things sometimes go wrong not in moaning about a bad board or asking how to bid a cold 4S! This response gives me a comprehensive understanding.

Firstly to make it clear I have no interest in a ruling just some clarity to better understand laws of bridge viz a viz alerting Board 1 of 24 Board KO match against very strong opponents (I would say our chances of winning at 10%) 1D-2D-2S-4H 4S-P-P-??? 1D natural (at least 4, playing 4c majors) 2D ostensibly Michaels, majors but opponent admits (online) "sorry I was raising partner's 1D so it's a mistake" which you could say is kind and ethical. 2S - natural but, in the light of 2D my RHO must be expecting it to not be 4S - RHO might be thinking they must be in a 6-2 5-3 or 4-4 fit and partner's 2D bid is based on 4c major. X or P - I don't know if he is obliged to double (for partner) holding 1-5-4-3 with Q and A in minor NB we actually missed the cold 4S (5-5 fit) by being a little flummoxed - s**t happens but wondering if anything is "expected" to be alerted to opponent or failing to alert is accurate because we bid naturally. All's well that ends well anyway as we managed to overcome a 35 imp deficit after 16 to win by 5 making this an exercise in dealing with this problem. Any ideas on whether 2S should be alerted? Is failing to alert telling RHO 2D was a mistake? Should the board be cancelled? Should the final contract be doubled? So many questions!

You are about to suffer a diamond ruff (and an ace of hearts or A or King spade later..) Suggest you bid the making 6N.