ATTOM Tax Assessor History - tax assessment history date

What is the difference between the following two data points in Tax Assessor History dataset?

ASSESSORHISTORYYEAR
TAXYEARASSESSED

They seem to mostly be the same but often are off by a year or sometimes more.

Which one should we use for the year that the property assessment took place (e.g. the year that the actual appraisal / new valuation took place)? Also, is there a way to get the actual date of this appraisal (month, date, year)?