@raymondtaylor , agreeing with the response from my colleague @Bsch4477 , there is always a middle ground. If you don't have the documentation to prove your case, you can still make a "best effort" valuation and as long as you have other supporting documents/ facts to show that you used all reasonable approach to come up with " reasonable" purchase/ acquisition cost, IRS will consider the basis. So my suggestion would be to document how you came up with basis figure. Of course there is always a chance that IRS may reject your "best-effort" figure and take the "zero" basis approach. So do the best you can and keep all documentation to back-up your claim.
Good Luck
