Not refittable for any cargo?

[stfrbrntyu]

I was looking for a (small) generic tram set which could be refitted with any cargo, your description says it can, but in FIRS 3 it only shows for 3 cargos. FS, ES, and goods.
With default industries and BSPI only goods and valuables.

I tried different years and different tracks, which gave the same result. Am I doing something wrong here?