How can I design or propose these apartments to meet this requirement while making them functional for long-term residents?

Their support app seems to function poorly or they may just be understaffed and can't respond or reimburse for other reasons.  1.

When I hear of historical significance, I think of an old building with significant cap ex, and functional obsolescence.

Not a major rehab - flooring, paint, and some misc. work  - not a full blown renovation.PS: I wish BP could really have a search function because the current one sucks. 

I also converted the other side of the property (it's a functioning duplex) into an Airbnb / Short Term Rental.

@Timothy Fortin As Michael's superb content here and elsewhere emphasize, cost segregation services are tightly intertwined with broader tax functions typically provided by accountants.

They tried to help without broadcasting their personal information and getting heaven know who contacting them to prove something they are part of but don't promote for a living, like our office staff. 

The city approved rental license inspector essentially just tested to make sure there was access to hot water, access to heat, no unsafe conditions like exposed electric wiring, CO/smoke detectors present/functional, fire extinguishers present/not expired, etc.

Doesn't Buildium have an accounting function though?

Once you have a shortlist, sign up for an account with each one and test them extensively to see how they function.