note that in addition to being a gun maker and skilled gunsmith, Schaefer was also sales agent for h&r an others, including Charles daly, who was also associated with Francotte and linder...
anybody else besides me, raimey an Campbell, getting the European licensee connection yet...
once h&r's exclusive license expired, then the American market was open to other licensees located in europe and America...
lots of buying, selling an trading goin on once h&r was out of the picture...
Ed, you need to read your own description before sticking to the idea that this gun was built by Schaefer. Once again, you said it had a low serial number of 25 which would make it built around 1882... three years before H&R's license expired. The dates aren't adding up to support the notion that Schaefer built this gun. You'll also need some evidence that Schaefer used H&R buttplates on guns he built, which is rather unlikely even if he was a sales agent for H&R.
If I was you, and this gun is a consignment, I'd contact the owner to check on the possibility that the original 10 ga. H&R barrels are still in existence. Then you'd have a complete H&R 10 gauge with a spare set of sub-gauge barrels.
It could be worse... From Argo44's post, you could get the idea that the European licensee connection indicates it was built by Reilly and his 300 or so imaginary gunmakers, using a Schaefer sourced rib, Belgian tubes, and an H&R buttplate. We all love wild speculation and conjecture here! Good luck with your sale.