To reduce the chance mistakes are made, take the records that you "know" are for your person of interest and estimate whichever items you do not have specifically:
- a time frame for when they were born
- an approximate location for where they were born
- a time frame for their marriage
- an approximate location for their marriage
- a time frame for their death
- an approximate location for their death
For all of these approximations, include your reason why you think the time frames and locations are reasonable--you should have at least one source document. These reasons combined with the records are key.
Then look at the "new" records you think are for your ancestor. How closely do they match your expectations? Is the difference reasonable? Is it possible your conjectures were wrong?
It may also cause you to question whether the records that you were "sure" were for your ancestor are really your ancestor at all.
We've simplified the analysis process here--but this general framework, armed with analysis and contemplation, is a good start.