If a question of paternity is riding on it, it would not be too cautious for both parents to get their blood type
checked with new tests. Then have the child's blood
tested (again) as well. This is to prevent jumping to conclusions. A lot of grief could be prevented if the couple were to find out their blood types weren't what they thought.
For example, my husband's blood type is A, why does he know this? Because he thinks it was on his Army dogtag 30 years ago. Mine is O.