"Should it have been amortized."

Amortization and Depreciation are processes that generally account for "starting value with changes over time that are a result of loss of that value, so let me write off part of it, each time"

"Now client considering selling the quota."

Which is likely why you treated it like land = does not Wear Out over time, has basis against future sale, and is subject to the Marketplace for ownership. For instance, land, and separately, the perpetual easement.