These people were buried in Oak Hill Cemetery, also known as Olean Cemetery. It seems to be a different Joseph, but he was also born in Canada. If Harriet were your Joseph's wife, then he would have had to abandon her and go to Michigan to marry Matilda. Seems a stretch, but stranger things have happened.
SIMPIER, Caroline J. Died, Oct. 8, 1875 age, 18 b. Olean, NY
SIMPIER, Harriet N. Died, Nov. 26, 1899 age, 65 b. Farmers Valley, NY
SIMPIER, Joseph Died, July 7, 1876 age, 56 b. Canada