All tax data is a "push" from the local jurisdictions to real estate data companies such as CoreLogic. While transactional data is pushed out on a continuous basis throughout the year by most jurisdictions (monthly or every few weeks), annual assessment data is typically pushed out only once per year by the jurisdictions.
For both transactional and assessment data, real estate data companies like CoreLogic must await the data to be pushed out from each jurisdiction. Based on past history, CoreLogic has a general idea when each jurisdiction will push the data, and they schedule resources in anticipation of these data pushes. Once received, CoreLogic loads and tests the data, then releases it in Realist as soon as possible for MLS users.