When JIRA Enterprise licensees were migrated to the new licensing model, they got a grandfathered equivalent 'unlimited' license. This means that JIRA reports unlimited for user count, which means plugins using that for license size validation also report unlimited.
In this scenario, where the actual users are somewhat less, say 400, and would naturally fit into the 101-500 user bracket, and would then allow plugin licensing tier to be more appropriate. Does Atlassian support 'right/down sizing' of JIRA licenses to minimise ongoing costs of plugins? Making plugins ignore reported license count seems... wrong.
As a side note, its also unclear how the new Marketplace license management deals with grandfathered licenses (not in the marketplace FAQ).