Hi Lou
The problem is that it is a marriage in January before Britain and her colonies adopted the Gregorian calendar. Which means we are not really sure whether the marriage took place on 6 Jan 1690/91 or 6 Jan 1691/92.
Unfortunately because the source is a transcript of marriages organised according to the surname of the groom, we can't see the dates in order, and in any case with transcripts, we often aren't sure whether they have transcribed exactly what is on the original record, or have already made an adjustment to the year, to take into account the fact that the Gregorian calendar isn't yet in use.
Having said that I do think you are correct to change the date to 6 Jan 1691 because that is what is stated in the only source we have so far, but I would add a research note to the biography just to indicate that we can't be sure whether this is 1690/91 or 1691/92.