For Federal purposes, you did exactly the right things:
Print and keep a copy of the KBB valuation, the Repair Estimate to establish a Valuation.
Print and keep a copy of the Scrapyard Valuation.
Print and keep a copy of the Actual transfer price.
Cartwright, 411 US 546, fair market value (FMV) is defined as “the price at which the property would change hands between a willing buyer and a willing seller, neither being under any compulsion to buy or to sell and both having reasonable knowledge of relevant facts."
The ideal FMV is your “Net Proceeds from a well attended auction” but most owners of low value cars don’t go that route so instead you have 3 defendable alternative valuations.
So assuming that the vehicle has been disposed your most likely FMV is either the Actual Sale Price OR the documented Scrap Value, WHICHEVER IS HIGHER.