Roman Catholics do not repeat valid baptisms. This is pretty simple easy:
480. The sacrament of baptism cannot be repeated and therefore it is not permitted to confer it again conditionally, unless there is a reasonable doubt about the fact or validity of the baptism already conferred. If serious investigation raises such prudent doubt and it seems necessary to confer baptism again conditionally, the minister should explain beforehand the reasons why this is being done and a nonsolemn form of baptism is to be used.
The local ordinary is to decide in each case what rites are to be included or excluded in conferring conditional baptism.
I knew of a case once in which a college student and his maternal grandmother said he had been baptized in a Catholic church as an infant. His Catholic mother died soon after, and there was no record of a baptism in the parish. The current pastor recalled the priest who baptized him was something of a maverick–an order priest for whom it wasn’t a surprise he might not submit proper paperwork.
There was no doubt about the fact of the baptism. There was just no record of it at all.
Note that conditional baptism is seen as a matter grave enough in which the bishop must weigh in each time it is done.
Catholic Sensibility 
There are many cases where Baptisms were not valid which might have been the case as well. If the baptism is not performed “In the name of the Father, Son, and Holy Spirit (Ghost)” it is not valid. The liberalization of the Church years ago led to some performing it “In the name of the creator, redeemer, and sanctifier” or some variation of this. They were declared by the Vatican to be invalid back in 2008. There was a great article about this here –
http://www.catholic.org/national/national_story.php?id=27028
Unfortunately, certficates of baptism are not necessarily conveying what they once were thought to convey – this is one of the unintended effects of creative baptismal formulae that sprang up in the past generation (not just in Catholic parishes but in mainstream Protestant ones as well), and I suspect that more due diligence is going to be required in the future. This is one of those fruits of not thinking things through fully.