CoreLogic bought Marshall & Swift and Marshall & Swift/Boeckh many years ago, CoreLogic is rebranding to Cotality.
"RCT" is their software for residential insurable replacement cost estimate, "Commercial Valuation" is for commercial and Ag (fka BVS - The old Boeckh software).
These are "reconstruction" cost basis.
Competing and acceptable options are e2Value or 360-Value.
If you're using the MVS or other hard copy books, you're likely using cost data that isn't for insurance purposes.
These are "new construction" cost basis, which will typically generate a lower estimate.
Your professional liability insurance likely excludes coverage for insurable value estimates.
Don't assume - ask.
The lenders have been allowed by Fannie to accept the inappropriate cost basis "cost approach" estimates to satisfy their documentation for minimum acceptable insurance requirements.
This is for acceptance to be able to sell the loan into the secondary market: it would not be adequate to protect the borrower in the event of a total loss.
Insurance agents, brokers, and underwriters all have access to the appropriate tools for insurable value estimates.
Loan servicing companies have the same software as well; they use it for auditing insurance limits on in-force loans.
So, why do lenders ask/demand the appraiser for an insurable replacement cost estimate?
a. They like the lower number because it makes the loan easier to close.
b. It's less work for them and it's good enough to sell the loan into the secondary market.
c. They don't know why, it's a check box on a form.
You can't stop the lenders or others from misusing your cost approach for insurance purposes, but disclaimers are recommended.
Could you agree, for an extra fee, to collect the data points they need to generate an insurable value estimate? Sure, just ask them what they need.
I've given this sermon enough times on this forum. Have fun.