According to Fedorin 143 variant was only in sets. If you are into microscopic differences, are you sure that your coin is not Fedorin 139 or 140. You are asking only about number assigned to one side of coin and miss F-91 variant for that side.
Likehood of getting premium for Fedorin 143 is minimal, if you can't prove it and can't find buyer willing to pay that premium.