when satellites delete pieces can they tell if it was test data or actual data.
The satellites, like the SNs - but for a different reason-, are blind to the content stored. Data pieces are uploaded independently from satellite control. A satellite sends a list of SNs to a client, the client encrypts the data and uploads the encrypted data pieces via a direct connection to an SN.
There is no technical difference between test data and actual data to begin with, that’s just the purpose us mere humans attach to it. It’s both data. And when it leaves the uplink it’s a blob of random noise as a result of encryption. I believe the metadata the satellite receives is encrypted as well, so there is absolutely no way to tell it apart.