Thanks everyone! I bought an extra RS485-USB port to cover me, but as a backup for our lights-up party now I know I can get a phone line and lay it out for a quick fix on the end box if part of the show should go dark while everyone's standing there. :-)
I have two CTB16PC controllers, prebuilt, in NEMA enclosures in the yard. On both of them the center port (leftmost RJ-45 port) is either squirrely or doesn't work at all, depending on the day. Is it possible to insert a network switch downstream from the RS-485 adapter so I don't have to daisy-chain? That way I could just use the other port on each controller. (I can have one bad port right now and place that controller at the end of the chain, but not two).