Sorry, but that really is an "old wives' tale". First, there is a simple mod that involves installing a check ball in the base plate to stop the backfire failures.
Second, if the car is set up and running right, you won't backfire on starting.
I'm probably the only guy you will ever meet that personally put over 80K miles on his A12 Roadrunner and yea, I popped one once. Pretty simple to fix, remove the front carb, float bowl and metering block on the main carb and that's it. That's the only time I ever had to lay a wrench to the carbs, except for a couple times pulling them down over the years to replace gaskets because it was time.
So, other than the myth of popped power valves that went away years ago, there's nothing magic or mystical about them. Almost all the problems I've ever seen with the carbs has been either ignition related (and blamed on the carbs) or owner related in that they had no business ever touching a carb. I find the same to be true with a lot of Thermoquads also.