The recording's are pooled together in the world of 360/Horizon software, it wasn't designed for this and has been adapted for the UK.
If you go to Recordings > Recorded > View all > and click on the Recorded tab you will see a drop down with the following options:-
Recorded, Recorded on this Virgin TV box, Planned, and Planned for this Virgin TV box. - highlighting "Recorded on this Virgin TV box" will just show those programs recorded on that box.
You can make the 360 record programs on predetermined boxes.
When setting up a series link go to Advanced and select which box you want the recording to be made on. It will then be recorded on that box going forward, even if the default recording box is the other one. So all you need to do is reset your series links to record on the box you want them to.
Unfortunately to reset the links, you'll need to delete and reset. You can also use the same method to record individual programs rather than series.