If you have assigned a System Quick key to each county, you could disable the third one by pushing the . No button, then the number you assigned, then the Eyes button. It will tell you that that number is OFF
Somewhere between 10 and 20 Frequencies/TGs, I start to imagine that I am missing more transmissions than I'm hearing. So, when I get to that stage, I divide the Freqs/TGs up into two favorite lists (or whatever the scanner brand calls them). If I want to NOT MISS MUCH (while at home), I assign a single FL to 8 City PD TGs, another FL to 10 local FD Frequencies. For expanded County coverage, a FL for 8 DPS Frequencies, and another FL for 10 County Public Service TGs. Another 20, or so, FLs for additional special interest agencies. I setup all scanners basically identically, allowing rapid isolation of a developing HOT emergency channel.
More FLs, less objects in each. The only way for me.