The Improved Tithe Barns for Mongols has exactly the same text as the normal Tithe Barns… it seems to give +45 food/+45 Wood and +30 Stone instead per min per relic garrisoned, however.
(normal ones text is +20 food, wood and stone per relic garrisoned)
I was just reading through all the text for Mongols now its been mostly sorted out and noticed this is still not showing its actual benefit.