Hi Tim,
Are you sure that all these companies are related?
The "successeurs" itself does not imply it unless the guns or catalogs would be marked something like:
"Xxxxx F. Darne Successeurs" ( Also possibly abbreviated as "Succr")
"Yyyyy Successeurs" by itself just would say the brand Yyyyy belongs to a new owner but the entity name is unchanged or little changed.
Many firms made or retailed Darne like guns and they did not need to have any connection to Darne, after the patent had run out in the early 20th century.
Unfortunately, I don't have any relevant catalogs.
Best regards,
WC-
