I'm telling you what I did to get my property tax lowered via the online portal earlier this year. Yes the pdf explaining the appeal process says the appraisal for financing is not admissable as evidence before the tax board unless the appraiser is at the hearing. But I submitted the appraisal as evidence and the assessor settled before a hearing.

My sale was outside the October - October date range. So were all of the comps in my financing appraisal. My appeal was still successful.

You're correct on the 15% threshold, good call there.

I'm sure for more complex property tax appeals or for higher value properties you need an appraisal where the purpose and use is a property tax appeal, but for a 1 or 2 bedroom condo with a recent sale price that shows the assessment is wrong by 15%+, my experience is the assessor will lower the assessment if you file the appeal yourself.

Edit to say your post makes a lot more sense when I see your other posts are advertising for tax appeal services.