dlloyd:
As long as the voltage is within spec AND the current is within spec, then the life expectancy will be within spec.
That's better, but it's just the current you're worried about.
dlloyd:
I wasn't quite specific enough...not current limiting. Just equivalent resistance @ 12V.
An ammeter would be useful to check the rate of current rise .. it won't register until you get near 9V, then it will climb to 1.05A as the voltage increases towards 12V.
The spec states that the Vf is between 9V and 12V. A single, particular LED from the batch will be in spec if it consumes 1A at some voltage between 9V and 12V. That could be 10.4V, 11.7V... you don't know, and it's going to differ between multiple LEDs in the same batch.
If you follow the method of finding the voltage that the LED consumes 1A at then you add two additional considerations: You have to make sure that the temperature of the LED stays constant (Vf drops as temperature increases) and you also have to make sure you periodically check on your LED every week or so because the Vf also changes with age. It can be done but it's a lot more effort than driving it with constant voltage.