Your cashback may even become zero if you manage to recover and make a profit before the day of the cashback distribution. I said it based on my own experience few weeks ago when I had like $20 cashback under my available rewards on the VIP program page, but it was gone a day later because I managed to win back and make nice profit. As what you say, cashback is based on netloss unlike rakeback which is based on wager amount.
If I am not wrong, if you claim that $20 cashback and then you win back what you lose, then if you lose again, you won't get the cashback till you pass the previous limit. For example, if your loss was $500, this time you won't get cashback until you lose more than $500. If I remember correctly, one of the casino support explained this a while ago.
But as far as I know, different casinos have different systems. Some casino has a cashback expiring system. Users have to claim their cashback within a certain time, otherwise the cashback expires. Some other casinos do not have an expiring system.