[Tagging] Landfills timespan

[Cascafico Giovanni]

Hello,

I've an OSM compatible dataset that helps me to spot landfills. Older
ones are already covered by grass and/or trees.

IMHO could be useful to save landfill locations for a future possible use.
Does it make sense tag the ones with surface alterations with level=-1 ?

Or shall I consider landuse=landfill as a functional tagging, hence
tagging them abandoned:landuse=landfill?