Jay, and all CRs:
I can't comment on the variability of hook-bead rims, but I've had a similar problem of having new kevlar-bead tires blow off of clincher rims, (Michelin, Matrix, Vittoria on MA2 rims) even if the rim and tire are correctly matched.
Consequently I "break in" a new tire to prevent future blowouts:
I install the tire on the rim and inflate to 1/2 pressure. I then deflate the tire completely, and then I roll the wheel with the deflated tire about three revolutions forward, and then three revolutions backward, while putting pressure on the hub axle.
As far as I can tell, this gentle mashing of the tire bead into the rim well "breaks in" the sidewall of the tire adjacent to the bead, which (I suspect) helps the bead be more flexible adjacent to the rim hook and consequently give a more secure fit.
I usually haven't had a problem with a tire that has been ridden a while but a couple of months ago I had a well used Vittoria CX blow off the rim after reinstallation. So, I now do this seating/break in process on every tire, new or used.
regards,
Andrew Gillis (pending rain tomorrow in Long Beach, CA)