OK - I tested this myself
Sol B can indeed be reused. I am on my 5th film now and everything works perfectly. Today I developed four films (2 Fomapan 100, 1 Fomapan 200 and 1 APX 100) in the same 1 liter tank with the Sol B I used for the first roll, and they all came out very nicely.
Great developer all round.