wblock,
By "select" do you mean the road numbers/addresses in your recall stack? It sounds to me that your Power Cab has a recall stack of "2" - i.e. if you keep pressing the RECALL button only two locomotives will show on your Power Cab's LCD screen.
You can re-enter other locomotive address into your Power Cab; it will just overwrite the last address. The info for the other locomotives on your layout can still be called up on your Power Cab.
If you want to have a recall stack larger than two addresses (you can have between 2 and 6 on your Power Cab), your Power Cab manual will show you how to do that. I generally keep mine at 2 or 3 addresses to minimize the amount of times I have to press the RECALL button to get to the locomotive I want. Besides, it's just as easy (and sometimes qucker) to enter a 4-digit address if the locomotive isn't in the stack at that moment.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
For some reason my Power Cab now recognizes only the last two locos I selected. If I try to select any others nothing happens, but this has only started recently. All the others were working properly until just a few days ago. This is a total of four others on a very small layout. The two that it does recognize are working fine.
Even at the beginning of a session only those two are recognized.
I'm not sure what other information you might need to help diagnose the problem.