There have been variations of this question, but replies don't seem to help me.

My parents are in their late 90's, Mom did the "bookkeeping" for stock transactions until her 80's, but very little info has survived several moves in the past 20 years. I need to sell some shares for them, however, I have no idea how to handle the calculation of capital gains. Some of the stocks were bought back in the 60's, 70's and 80's. Mom doesn't seem to have kept confirmation statements (or they've been long lost). She does have a very old notebook where she recorded some dividends. The records end a number of years ago and the starting data seems sporadic at best. Bottom line, I have absolutely no idea when they were purchased or for how much. To add more confusion, a number of companies had their dividends reinvested. Hopefully you get the idea.

What does the IRS expect in the way of data on the tax return? Some of the investments (like IBM going back to the 60's) must have a very low cost basis at this point. Do I just make up a date and put the cost as $0? Would the IRS accept that? Or do they have a standard way of handling such situations?

My strategy is the just hang on to as much of the old stuff until they pass away - the whole cost basis issue would then not be an issue. But some of the investments do need to be sold. And this being December, there are one or two companies that seem to have a loss (I know approximately which year(s) the stock was purchased, but have no idea as to specific date and cost).

Any suggestions would be appreciated.