A relative giving information for a record could easily get similar (or not so similar) names confused.
Any chance a relative got the names John and Tom confused? These are not the same names, are not derived from the same name, but a mixup could easily take place.
This is more likely the case if a minority of documents give a name that does not appear anywhere else.
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It is easy to get confused and say the wrong name even when you know better. An example was my mother, a teacher — she “called the roll” when calling for me — her younger sisters' names, the older nieces' names, finally getting my name right. And I was an only child!