When using MarketplaceService:GetProductInfo on a UGC limited the IsLimited key is set to false.
Reproduction Code:
local ITEM_ID = 13455546043
local Info = game:GetService("MarketplaceService"):GetProductInfo(ITEM_ID)
print(Info.IsLimited) -- gives "false", should be "true"
The top-level IsLimited and IsLimitedUnique fields are not being populated for UGC items. Please refer to the fields in the CollectiblesItemDetails object.