Varies by area but anything modern is hot right now.

pool surface with modern material maybe 25 years (old plaster lasted longer than the newer surface material). 

they can be more efficient than modern high-efficiency furnaces in some cases but they take a bit of maintenance and the radiators can be cumbersome in the rooms.

With the house being so old it absolutely would not pass modern inspections.

I’ve seen some pretty bad stone basements in my days that need to be completely redone in sections with modern block replacement.

When you have an older outdated bathroom, converting it to new and modern will most likely increase your property value (forced appreciation).

I don’t think there is any historical precedent in the modern economies for this, or is there?

They're modern and clean.

Good morning and Happy Thanksgiving,Are you a modern home builder in Washington, DC?

And in CA laws in many counties have changed see  LA county that those lots created before 1920 must meet modern lot standards to be recognized again.In Portland were I work its much easier and its one of the ways to really makes some good dough when the seller does not realize they are sitting on multiple lots that just need and over the counter lot confirmation to revive the existing lot and make it buildable.but in your instance, it sounds like At the county / city level they are not recognizing the underlying lots.. there for the contract cannot be prosecuted and closed as written.