Which object IDs can be used as unique identifiers?

[Pazyryk]

I'm trying to figure out which have IDs that I can safely use as unique identifiers in Lua.

So...
playerID -yes
civID -no (can be repeated if you have only 3 civ types and >3 players)
plotID -yes
cityID -no (but can use plotID as unique identifier)

Are UnitIDs unique across game or are they iterated within each player?

 

[Gedemon]

UnitIDs are not unique, like cities