Desktop Central <-> Service Desk Pro Integration question on Asset

Ok, so If I have an existing asset in SDP and then add it to Desktop Central, what is the common workstation field that binds Desktop Central to update it in SDP? For example, I added a new asset into SDP with ONLY the same hostname as it already appears in Desktop Central but doing a scan now on it doesnt update it.

As a test I added a new system to Desktop Central, which then created the asset in SDP. It stays updated. I've removed all the info on that asset and it still stays updated from Desktop Central.

I just want to know what data is missing from an existing asset in SDP that is preventing Desktop Central from updating it (again both SDP and DC have the hostname the same)