Precisely. It’s a testing phase. It doesn’t mean that the last day of testing is their final iteration of it.
They may look at the last days worth of testing and think “hey, this needs about a 10% buff across the board” and then it’s released 10% stronger than you remember it being.
This is apparently what happened on the PTR. It was a bit too easy with a bit too high of success rate for a challenge mode. So they stealth buffed it.
Apparently the buff was a bit too much for too many people. They could dial the stealth buff back 25-33% (so a 66-75% buff is still active from PTR). In my humble casual self opion