People once gave me skins all the time, they would be in a Walmart bag leaned against my garage door, sometimes I never knew who dropped them off and never heard from anyone, people just knew I needed skins.
Once I found two gigantic canebrake skins left at my door, they were a little old, faded and boraxed to the hilt. I put one on the Trad Gang St Jude auction giving in detail its condition, it went for around $50
I decided to use the other one on a bow my nephew was making in the shop, I washed it and scrubbed for at least a half hour to get the borax out. Once wet I found that it needed fleshing, I bet I took a half pound of meat off it before I was done.
Like you I found that this old neglected skin handled properly made a really nice backing.
Here is my nephew and his bow, I have posted this picture recently.