Make it work. You (or your client) must have some idea of the original sales price. Make your best educated guess. Ideally you request a copy of the original return from IRS to confirm.

There is no way to "make it work".  The installment sale was inherited so the current client is not the one who sold the property.  There was ordinary income recapture, depreciation and would have been selling expenses.  We have bits of information, but not enough to back into what would have been on the original 6252.

There are ways to "make it work", be creative or do the work to get a an actual transcript or copy of the original return. https://proconnect.intuit.com/community/lacerte-tax-discussions/discussion/6252-prior-year-info/00/9...

Hmm.  I expect the legal hoops to be able to get a 2005 return for a deceased taxpayer might be insurmountable by my 9/30 trust deadline.  So I'll have to go with alternative A.  Thanks.