I can now "Hire Old Allies" for Play Coins in the original version of Find Mii. I thought this was new functionality that appeared with the most recent update, but other people have the update and can't hire old allies in Find Mii.
Both my 3DS (Ver 6.2.0-12U) and StreetPass Mii Plaza is updated to the latest version. I have 148 Play Coins. I also recently earned the "Completed Find Mii five times" Accomplishment.
What are the conditions to unlock the hiring old heroes in Find Mii?