Update: I did some more Googling, and found it not to be that easy at all. Especially not here on WCG where the project servers compare a lot more of the device info than other projects. So it's just a matter of waiting and hoping then.
https://boinc.berkeley.edu/wiki/Host_identification_and_merging

Just curious: How long a time period is a "seek" ?
Cheers

Unfortunately, it's not that easy. Both parts of the system (server and client) gather and compare many parameters allowing easy identification of returning device. One of them - the most important, from my experience - is connection counter, so called rpc_seqno located in client_state.xml
Every time the client connects to the server, this counter increases and server compares rpc_seqno stored on his side with rpc_seqno reported by the client. If the number on server side is bigger than on client side, the server refuses connection and makes client to register itself under new host-ID. Only if rpc_seqno on client side is equal or bigger, the server accepts connection and everything goes smoothly.
The reason of such behavior is pretty simple: smaller rpc_seqno on client side than on server side means that data on client side are not current - the client reporting smaller connection counter cannot be the same which connected just before and set connection counter on server side to bigger value.
Reverse situation is perfectly OK - client could try to connect (increasing his rpc-seqno counter), but the connection did not succeeded (e.g. due to network problems). No connection, no risk of having outdated client, we can connect and work!
In your particular situation, you need to find out what number put in rpc_seqno parameter. It must be bigger than one stored on server side and it depends on how long your client was active and how frequently it was working. E.g. on one of my most active systems, online since December 2007,rpc_seqno is around 320k and I estimate that it increases by 30k every year (I had a copy of client_state.xml from 2012 and rpc_seqno there is around 20k)

There's some custom WCG code (well, quite a bit actually) that differs from the original BOINC code, and one of them is hostID matching. There is a WCG Wiki article somewhere (do a forum search) on the custom process WCG uses to see if a new device matches a pre-existing device.

Unfortunately, it's just not that easy, and often times you'll end up with duplicate devices in your WCG profile even if it's the same computer (e.g. after you reinstall the OS). BOINC allows the user to merge or delete devices, but WCG did away with that when they customized the code.

I would love to get rid of the WCG custom code and be able to merge devices as well as delete devices that have 0 results, but I've been waiting 10-15+ years.