The valuation date: why last month's sale may be the wrong evidence
An assessment speaks to a specific date. Evidence has to speak to the same one.
Assessments are not "as of today". Each assessment year has a valuation date, and everything is judged as of that moment.
Why it matters
A sale six months after the valuation date reflects a market the assessor was not permitted to see. If prices moved between the two, your evidence and the assessment are describing different worlds, and the assessor will say so.
Which direction hurts you
In a falling market, recent sales look helpfully low but post-date the valuation. In a rising market, recent sales undercut your own case. Either way, evidence closest to the valuation date is the evidence that counts.
What to do
Ask the assessor or Board of Review what the valuation date is for the year you are appealing. Then prefer sales in the window around it. If you must use a later sale, say so and explain why it still speaks to the earlier date.
Uniformity sidesteps this
Comparable assessments are all struck as of the same date by definition, so a uniformity argument has no timing problem at all. It is one more reason it is often the cleaner case.