After reviewing all the recordings last night this is what I found:
60150 is being used for King county. (unit ids in the 15000s) The furthest east was Rt 18 and I90 junction around Preston Snoqualmie area.
60108 is Snohomish County. (Unit Ids in the 13000s) It seems to be east Snohomish. Rt 522 from the county line to RT 2 and then east of Route 2 to Index.
I have not heard any locations for the west part of Snohomish
60120 Might be Skagit county, (unit ids 12000s) Heard a couple locations for I5 up there. Anderson road, Mile marker 221 and 225. Not a lot of activity.
60150 was the most active