Owning several parcels: check them together, appeal them separately
Assessments are individual. Reviewing a portfolio at once shows you which one is the outlier.
Owners of several properties frequently assume their assessments are consistent with each other. They are usually not, because each was set independently.
Review as a set
Compute assessed value per square foot for each parcel you own and put them side by side. Wide variation between similar properties in similar areas is a signal — one or two are usually the outliers while the rest are unremarkable.
Appeal individually
Each parcel is a separate assessment with a separate appeal, even under one owner and one deadline. There is no portfolio appeal, and a filing covering several PINs without separating them causes problems.
Prioritise by value, not by grievance
Rank by likely annual saving multiplied by the years it will persist. Appeal the top of that list. Filing on all of them costs effort on parcels that were fine and exposes each to review.
Entities
If the properties are held by an LLC, remember that at PTAB an entity generally needs an attorney. At the Board of Review a member can usually appear — check locally.
The record-keeping benefit
Doing this once gives you a baseline. Next year you compare against your own figures rather than starting again, and outliers announce themselves.