A little question if I may:
How many reminders have there been sent out since this started?.
There comes a point when sending out reminder after after reminder, becomes futile, as there will be those that will just file the thing in the Out bin.
In my own opinion, those that have a need to be certified, should be by now, they have had ample time to get with the program.
Anything less, just screams, I can't be bothered, I have no respect for the trade I work in.