See:

http://www.syracuseuniversitypress.syr.edu/spring-2010/pulling-strings.html

I have spoken with the author. Well researched and interesting. I have also repaired many Clark Irish Harps

Meville Clark died in 1953. His harp business died with him. Most of the Clark harps that show up were built between 1915 and 1953, although There are a very few that are a bit older, but Clark was not building harps in the 1820's.
Arsalaan Fay