*Information from <<https://my.strathspey.org/dd/issue/2226/|issue 2226>>:*

This would be Thomas Skillern, died 1800, music publisher based in London. Not to be confused with his nephew Thomas Skillern (1776-1849), also a London based music publisher under the partnership Skillern & Challoner. Anything published 1800 or earlier is the uncle, anything after 1805 is the nephew.