According to the folks at the relevant county office, the value as of last January is what counts, plus or minus 3 months. The language of the forms used stresses this.
This is understandable, since values have fallen at least 10% since January for most areas. The Assessor naturally wants to not be too generous in lowering assessed values, so will stick to their rules.
I found the clerks at the County Administration Building to be very helpful and courteous, by the way. That may not last, as they are about to get a tsunami of appeals. They are already way behind on processing their current backlog.
