@Linda Weygant is the expert on Real estate and international tax. 

You even said so yourself: 10-15-20 years.But even without an end, there's a metric called Internal Rate of Return (IRR) that can tell you the estimated compounded rate of return over the life of the deal, even if the deal goes on forever.This is because there's something called Time Value of Money, where money earned later is worth less. 

The 50% number is either a LO that does not really know the requirement or it is there internal requirement for their non-conventional loan program. 

This dose seem odd I would say this is and internal policy so my guess would be that you can negotiate this as many are saying you are not qualified for there internal guidelines.  

Myself with Landmark Sotheby's International Realty, and MC Mortgage Group out of Wilmington for the DSCR loan.

Our internal guideline - If we don't plan on gut rehabbing (tearing down any walls, updating the electric, plumbing....) our contractor gets what's called an Easy Permit. 

This language will address a broad variety of issues and attempt to avoid and control internal disputes.

It more has to do with your willingness to do what it takes to meet the lender's requirements and the lender's willingness to make the loan based on their internal guidelines.

It's just very important you have a great property manager that carefully selects the students (usually graduate students or international students with unlimited pockets).

In addition to marketing to nurses I also emailed or contacted on linkedin all the major corporations in the area and tried to find the HR lead in charge of hiring corporate interns as they were usually 3-6 month assignments.