Multiple Handwriting on One Document

Look carefully at that next original document you see. Does it appear that the handwriting was all done at the same time by the same person? Or were things written over time. My grandfather's 1903 birth certificate was filled out at three different times. One person apparently wrote the bulk of the document when it was recorded in November of 1903. Someone else wrote his last name in later--the handwriting is different. Someone else wrote in his first and middle name--the ink color is slightly different as is the handwriting.