Do you know what caused them ? DISTILLED white vinegar added to DISTILLED water does well cleaning Chrome. (third vinegar). Especially if it was from salts.

I don't know what caused them. They were on the drum when I bought it used.

It resembles pitting, They probably realized that they wont't be getting rid of them and sold it for that reason.

Pitting starts under the Chrome and pushes it off. Not sure about wraps though. Can you feel it with your fingers ?

That's corrosion setting in inside/under the wrap. Not much you can do for it other than re-wrap it. The chrome wrap of this era was a plastic wrap, not "real" metal like the old "chrome-o-wood" was. Basically it was a base layer of plastic, a layer of metal foil, and a layer of clear plastic all made in a laminate, most likely by Delmar at the time. Moisture has gotten into the wrap and started the corrosion of the foil. Most likely cause by storage of the drum in a damp basement or the like.

Again, not much you can do to fix it other than a re-wrap in the same material or a different finish from the chrome. Fortunately it's a Rocker series drum so you really wouldn't be killing it's value by re-wrapping as it essentially has no real great value. Rockers were considered entry level Ludwig's at the time, so no big deal if you modify it.