I know your posting has been here for quite a while but I hope this information will get to you.
I have pictures of Irving Van Tassell which were in my grandmother's possessions.I am trying to figure out the connection.Her name was Louise 'Octavie' Boudreau and she married Simon Paul LeBlanc.She was from Yarmouth and he was from Pubnico.
There is a listing for Irving born June 8, 1898 as well as one for a Joseph born June 8, 1899.Interesting that you say your father Joseph Irving was born June 8, 1901.Hmmm???
Irving's mother is shown as Maggie and Joseph's mother is shown as Margaret.Fathers are normally shown on these war records as next-of-kin if they are alive.Irving's document is from 1916 and Joseph's is from 1918.
Irving signed his I Van Tassell and Joseph signed Joseph Van Tassell.I find the V in both signature strangely similar.