Never heard of this, but agree with Erik.
Try to view the crossover and look for pad down resistors checking their wattage rating.
The owner of a stereo shop (and myself) tortured a pair of the first 45 version for an entire afternoon in 1977 (just for fun when I told him I was moving to CA in a few weeks).
We blasted rock and classical running them with a big Bose amp and another power amp with little lights forming a "V" on the front (forget the manufacturer).
They survived while sounding good, but they were new speakers - not 40 year old speakers.
I'm guessing that a 10 watt rating would be fine for that speaker, but you could use 20's for peace of mind.
DeKay