No matter how assiduously you've followed the paper record it's worth keeping in the back of your mind the possibility that something undocumented happened.
Babies being inadvertently switched at birth is one of the less frequent occurrences, but it does happen. Twelve such events are given in this article; one relates to Ottawa.
Overall, proof by birth or baptismal certificate is never 100%.
- undocumented adoptions,
- mothers claiming maternity of their young daughter's child
- the supposed father not being the biological father (non-paternity rates are typically quoted as 1-2%).
Another case in a well written story at https://strangepilgrimage.wordpress.com/2015/01/22/and-who-wouldve-thought-it-figures/