How are property taxes estimated when escrowed?

[CJ M.]

At closing, when a mortgage company estimates the amount of funds needed in escrow to cover future property taxes, do they base that off the county tax % and the purchase price/appraisal, or solely off the prior year's tax bill?

So for example, if a property is BRRRR'd and bought at a discount initially, when the owner refi's it, does the bank estimate future property taxes off the new appraised amount, or the prior years tax amount (when the property was worth significantly less)?

Just trying to understand if BRRRR properties generally take a big property tax hit once the county reassess them in the future...or if the banks already account for the reassessments based on the purchase price/appraisal.