A grand lead

Another board from the weekend in Denmark ended very luckily for our side thanks to the good old advice of leading trumps against grand slams.

The opponent on lead held K742/742/965/J82 and listened to this auction:
1D - 2C
2H - 3H
3S - 4C
4D - 4N
5D - 5S
7H

1D 11-15 various
2C artificial gameforce
2H 4H & 5+m (not 5422 shape)
3H supp
3S/4C/4H cue's
4N Parity Key Card
5D 1 A and denies trump Q
5S grand slam try

He lead a trump and this was the full deal (rotated).

E/EV vul
_________A
_________T963
_________KDT43
_________K73
JT953____________K742
D5_______________742
J72______________965
D94______________J82
_________D86
_________EKJ8
_________E8
_________ET65

My partner (not Frederic) played the system for the first time and forgot about the Parity Key Card response denying the trump queen. (There was also a mechanism available after 2H for finding out sidesuit & shortness.)

After the low heart lead, I naturally dropped the queen offside to make. The lead was certainly somewhat unlucky, but trump leads vs grand slams have a far worse track record than most believe.

There are some people out there who willingly bid grand slams (with split top honors) without the queen, expecting to get a trump lead solving the situation or otherwise playing the non-leader for it. On this deal, for instance, possesion of the queen was only implied; it wasn't explicitly shown.