According to a tree I saw at Geneanet (by Amanda Rowe) it said that Thaddeus was born at Campbell's Creek, NL in October 1861; and DIED at St-Pierre on 7 Aug 1936 (impossible to confirm this unless one writes to the Mairie of St-Pierre for a certificate).
I am also wondering how she made the jump from LaCoste/LaCosta to the Élisagaray family of Louhossoa (Pyrenées-Atlantiques department). It seems like a far stretch to me. Unless there is a connection in the record of Jean and Adele's son, Dominique born in 1859 (too bad there is no exact record available to consult).
I just spent about two hours looking at the parish registers of that place online (from 1809-1840) at the Pyrenées-Atlantiques departmental archives, and did not see any reference to LaCoste/LaCosta at all in any of the families' records registered there. There is also a Lincoïn family in that place, could members of this family have transformed to Couenne? I have no idea at present.
If you visit Geneanet, after signing in, look for a contact to member Amanda M Rowe
(Geneanet > Contacts> Contact Page> Amandamrowe, and send her an e-mail, asking her to share her sources with you, since you seem to be related. Best regards, Dennis