How do your negs appear? I mean in unexposed and developed areas...if they exhibit normal FB +Fog then I wouldn't concern myself. I don't know why 35 mm would be any different then sheet film. If my memory serves me correctly...it seems that 35 mm used to carry higher FB + Fog then sheet film. But it has been a long time ago and I may be wrong on that.
If Les has a densitometer then he could verify that since he still shoots 35 mm from what I understand.