You are absolutely right about the upgrade inventory. I need seats available in J class to upgrade from Economy using Miles&Smiles miles. As for I class I think it's for upgrades using another program's miles as you noted but don't have first hand experience. In my case the October 3rd flight...
Would appreciate if someone could look up the loading info for TK157 October 3rd and TK78 January 3rd. Hoping to upgrade from Economy P Class to Business Class..