Thanks for your answer @rjs.
To clarify, when the investments were transferred from the trust of the person we inherited them from, they were transferred to in-kind investments (where possible), and the original cost basis (purchase date and cost) followed them. Our brokerage does have this cost basis information and did list it on the 1099-B.
Yes, the re-investments occurred after we acquired them, due to that option being selected for the individual investments. Because of the timing some of them are long-term and some short.
After asking this question, I discovered why turbotax was asking me to review these investments: one of the sales was missing cost basis information. Our brokerage listed it as "unknown". After some research I found out that this particular investment was somehow 'spun-off' of a related investment when that company merged with another creating the new entity. I assume that the cost basis is just the fair market value of that security on that date?
