For what it is worth. I think it is unlikely/improbable.
In normal barring there is a dosage effect, so I would expect a gradual increase from 1 to 4 copies.
Dosage effect may be easy to detect at low copy levels but not at higher levels. My thinking that with increases in the number of copies producing a given product increases, in this case one that is likely regulatory, the increment of effects would decrease.
For example:
0 versus 1 copy - extremely large increase in gene product
1 versus 2 copies - double gene product
2 versus 3 copies - 50% increase in gene product
3 versus 4 copies - 33.3% increase in gene product
Difficulties of detection at high copy levels may be even more difficult in example since regulatory, dosage increases beyond a certain point may have no efffect if regulatory sites become saturated.
Leghorns were not autosomal barred. Is it not possible some lines were? Crossing over between chromosomes during development process for California grey certainly could have resulted in a an autosomal variant of locus coding for barring.
Another possibility certain to not exhuast all is that male B^sd / B not readily distinguishable from female B^sd/-.
This would be a good topic at the-coop.org. Probably so.