Mark, it is more complex than that as usual with Heuers ;-)
The val 92 movement started already with signed crowns which you can see on many examples.
The val 72 hexa no signed crowns, already the next batch similar to the val 92 mostly originally signed crowns.
Hexa differs also from move signature, we have two different ED Heuer signatures, but thats another story !!
Landeron 189 no signed crowns until the end of production, due to cheaper movement some timewitnesses say it was an eco model dedicated to gain popularity on the US Market.
Hope this does not confuse further !
Cheers
Arno

: Crowns weren't routinely signed until the second executions came
: along circa 1969 Arno. I suspect that many of the few first
: executions that do have signed crowns were changed because the
: new owner thought the unsigned crown was incorrect, whereas in
: fact it's the unsigned one that is right.