Hi! Welcome to the communities.
I pretty much always see 2 base snapshots on my SV Destination volume. The reason I'm aware of for this is after the SV transfer finishes, there is some post processing that occurs that involves the delta information gathered from the two snapshots. My presumption is the second base snapshot is only needed for a short time, but but sticks around until the next snapshot purge operation.
FOr the life of me, I can't find my source on this. I thought it was in a document concerning volume deswizzling, but I can't find it now. If anybody has it handy, feel free to post it.