Check your donation form settings under Tools-->Settings. There is a setting to Mark new addresses as primary which you may want to uncheck. We do not delete any prior addresses, but they may be moved to non-primary.

Some customers will setup a new address type to capture new addresses so they can review them as needed.

I will mark this as voting open as the idea still stands, in the meantime check your settings to see if you ensure your current addresses aren't changing/moving!