Footage is the quantity
Every cable price is a rate per foot or per thousand feet. A partial reel is therefore priced on what remains, and the original length is irrelevant except as history.
Percentages mislead
A reel at 'about half' tells a buyer nothing usable. 'Roughly 480 feet, measured by weight' lets them quote. Precision here is worth more than any other single improvement to a lot description.
Small lengths still count
Twenty feet of 4/0 service cable has a use. Short lengths are often the easiest material to sell to a contractor who needs a repair piece, but they have to be listed.
When a partial is only scrap
If the construction cannot be identified and the condition is poor, the metal value may genuinely be the best number. Say so and move on rather than spending a season trying to prove otherwise.