Thanks everyone who replied.

It looks like the problem is fixed but I don't really know how.

I deleted the C:/bb file from the new computer and transferred a new copy from the old computer. I ran the setup.exe file from the original PG 2025 flash drive and this time there is not a single N/A style in the Style picker. The only thing I deliberately did differently from the first time was to do a fast style rebuild instead of a slow one, but all the third party styles are being listed correctly.

Tony