Why the release exists
Cable bought by a utility or cooperative sits on their asset register. Until it is formally retired, selling it is disposing of someone else's property, whatever the yard foreman believes.
What the document should say
The owning organisation, the material described well enough to match the reels, confirmation that it is retired from service and free to dispose of, and a signature with a date and a contact.
What it does to the offer
A released lot is reviewed like any other surplus: construction, footage, condition. The release does not raise the price by itself, but without it there is no transaction at all.
Keep it with the lot
Send the release with the manifest. A buyer who has the document in hand can schedule collection immediately rather than waiting on correspondence.