Do not assume that only one person wrote on a document or record you are using in your research. Carefully look at the handwriting to determine if it looks consistent throughout the document or if multiple writers could have been involved. Census records and record copies documents in courthouses are generally written by only one person. Original documents (such as a death record, or records in a pension file) may have had more than one person who wrote the information on a specific page.
And if the different handwriting means a different person wrote the information on the document, it could be that there was a different informant.
And those informants may not have been equally reliable.