Help with date conflict

I believe these are my great grandparents. http://www.disnorge.no/gravminner/bilde.php?id=2889391 But the birth dates are different. I have Nils born in 1856 http://www.arkivverket.no/URN:kb_read?idx_kildeid=8301&idx_id=8301&uid=ny&idx_side=-63 I have Britha born in 1849. http://www.arkivverket.no/URN:kb_read?idx_kildeid=1915&idx_id=1915&uid=ny&idx_side=-6 I know they went from Skånevik to Uskedalen in their later years. Thanks Jim