About 40 years ago my father gave me 75 shares of Dominion Corp, now Dominion Energy. I reinvested dividends over the years, accumulating 390 shares which my broker sold in 2017. Recently the broker sent an accounting of this sale (1099-B) for my 2017 taxes, but with no cost basis for 350 of the shares. Perhaps Dominion has no records on share purchases before a certain date, and I did not keep the annual accounting. Over the years, dividends paid and share prices fluctuated considerably. Is there a way to establish or estimate a cost basis for those Dominion shares?