I just find it humorous that is all.
But basically this week = +10 or higher is fine. Same with next week. As the end of week chests opened up on the 21st to 28th are still “season 3”
From the 21st onwards, you should do a +15 for those weeks.
With scheduled maintenance on January 21:
Mythic Keystone and PvP chests that are opened this week reflect Season 3 rewards earned the prior week, and cannot be Corrupted, but may Warforge/Titanforge.
With scheduled maintenance on January 28:
Weekly chests for Mythic Keystone and PvP activities now contain Season 4 items, which are always Corrupted, and scale up to item level 475. Again, these items will never Warforge/Titanforge.