Cyberyeti, on 2019-September-16, 04:11, said:
You are not seeing this at all, I get a complete count assuming this lead of dummy's first bid suit is as I expect stiff, you don't.
You won't know if W is 3253 or 2254 at the point you have to make your critical discard (it's fine when hearts are 6-1)
In practice we will both play something close to your line if hearts are 5-2 as 7N will be played the other way up, and on a passive heart or club lead we won't have the information the diamond lead reveals.
Players make unexpected leads all the time. Against 7
♠, why lead a singleton (and potentially compromise partner's diamond holding) when partner doesn't have an ace, you have a solid heart sequence to lead, and if partner gets the lead, the contract is already down? Against 7NT, I would not expect a diamond or a spade lead, although a either lead would certainly make things easier.
Assume North is dummy and South is declarer at 7NT since South bid NT first. First, you have to overcome your shock that dummy has an 18 count in this auction. Then, probably expect a club lead from West so any expectations about a singleton diamond with East don't arise.
It is easier to look at it from East's hand. One round of clubs has already been played. If East started with 5 clubs, they almost certainly would have pitched a (useless) club (or 2) on a diamond winner. If so, when you play the 4th club winner and East follows suit, you know they started with 5 clubs. If East had 5 hearts, I wouldn't expect 2 heart discards which could set up declarer's possible 4th heart when there are easy club pitches to make.
If East has pitched a club, the 4th club winner will reveal the club distribution. If East never pitches a club, I would probably play them for 4 clubs. West may also help declarer by pitching a "useless" club which would reveal the suit split.