Well said Bonomax. If you were in my area, I would certainly want you on my team. LOL
I agree in part - but there is a need to be able to quantify and calculate what repairs and updates add to the 'effective' age - then the same for that age vs new.
But we're losing site of how the numbers are found - and that is basically the function of the market not a set formula - but everyone and his sister seems to have a formula they use that works - whereas the market is the only place that will prove or disprove it.
In other words - a 100 year old house that has been well maintained through the years will automatically had parts updated at different intervals, if not several items at the same time. Contrast that to a 100 year old house that has set empty for past 40 years, but well maintained, or the 100 year old home that has very few updates and held together with patchwork repairs, bailing wire and duct tape. In the Pinehurst area we have all three in the priciest parts too - not in the volume I'm sure there are in Jack's area - our specifically the areas where my sister lives in the suburb communities surrounding Boston.
They are all 100 year old homes - just in different condition - 'how' would we determine the effective age of each and what would the age adjustment be. For sake of the example - they are all 3/2 1800' with no functional obsolescence.
Short of a total rebuild - a 100 year old house will never have the same effective age as new. (of course it would be new if it was a total rebuild) That is in practical terms - but the market may show different it pricing.
The question is 'how' not why or how to handle the results after they have been determined or what they are - but how to determine the numbers.