it was during the game round. That will explain it than. Why not introduced with the update? The income is reduced a lot but still the same high amounts of money have to be payed.
'Income is reduced a lot' - how so?
If costs or prestige amounts are changed, those changes will be activated only in starting rounds and not in the middle of the round. This will keep the game balanced and the changes will not give anyone an edge. In the case of HQ, it would not be fair if one player pays only half to upgrade the HQ compared to another player who already upgraded the HQ.