The polydactyl trait has a lot of variation in expression. Too many toes is not that uncommon a trait. If an otherwise good bird it's okay to breed it, especially if you have any 4-toed silkies to pair it with. If you see extra toes recurring in chicks, then you may want to stop using the bird for breeding.
There is an extreme variation where an entire extra set of toes occurs on top of the foot. We had one of those who otherwise was an extremely nice quality. We gave her to a pet home where she could be pretty yard candy and get the extra atttention she needed (she much preferred to find and stay in one place than to walk--even to food/water).
Incorrect number of toes (too few/too many) is a disqualification: DQ.
No photos, my son got her from a friend, but he sorta lost interest and so I gave her to someone who would give her more attention.
I've only ever had one hatchery silkie, so I can't say. Odd numbers of toes occasionally pop up, and I'd rather deal with too many toes than with poorly separated toes. Of course I'd rather have all perfect toes, but what can I say--perfect birds don't exist, and most judges are satified with the correct number and don't really care about placement.
I expect the five toed breeds all have this problem, but since silkies are hte only five toed breed I raise, that is speculation and nothing more.