<VV> rubber brake adjust hole plugs

[Ed Dowds]

I've always felt that the rubber plugs were not needed. The knockouts are behind the wheel so they are somewhat shielded, but from what I don't know.
The plugs may keep water from entering but what is to stop water from entering between the drum and the backing plate?
Some may say that that area is a maze. That is true and it will stop splashing water, but how would splashing water get around the drum bonce off the inner wheel and enter the drum thru the knockout?
All of this splashing water problem becomes mute if the drum is submerged in water as the water will enter between the drum and backing plate.
I worked in a FLAPS many years ago when drums were still on both ends of the cars. I sold the plugs and may have even installed them if they came in a kit for my own brakes. 
I think they were designed for plugging the backing plate on other cars. They may have had a use there as splashing water would/could have gone directly thru the backing plates.
Ed