Thanks. the reason I asked is that there are some non-GS approved resellers that are not selling new product, but used or possibly new and they may have custom firmware that points the phone back to their config servers.
However, I am of the opinion that given the description provided. of the phone being used for several days and then later picking up a config seems to be more likely a provisioning issue. Manually provision the phone and turn off LLDP and CDP. Also check the router for DHCP options that might be used and see where they point. Additionally, clear the config server setting in the phone and then reconnect and see what happens.
It seems unlikely that the phone would have a profile with one set of parameters and then after a reset it would magically recall an old profile from an earlier period. If this were true, then it implies that you could power the device up using a transformer and then reset it and without doing anything else, it should somehow revert to extension 10. I am of the opinion that LLDP or a DHCP option is telling the phone how to get a config and the config is still available in whatever device it is being directed.