There are a number of caveats people need to be aware of when doing as you suggested.
Yes you can summarize. That's been available some time. But you do need to separate out certain items. I don't know everything here, but I wash sales are one of these. I put in two short term covered entries this year. The one wash and everything else. And you need to tell TT so it creates the proper code on the tax forms.
Cost basis can vary. For example if you inherit the stock, the cost basis will be the cost at the time of the decedents death AND is always treated as long term. So if you father purchased a stock in January 2021, died in March and you sell it in September, the cost basis in the March value and it is still long term. Unless this occurred in i think 2010 and there are tricky rules because of Congressional mucking about.
You do need to account for dividend reinvestment. That's reason I kept Quicken as it handles the cost basis for stocks I've held since the early 80s and I don't have to figure out the basis for almost 40 years of dividends.
I haven't run in to the situation but if you truly don't know the cost basis of some old stock, I think there are some IRS rules to handle that. You certainly don't want to use 0 unless you really have to.
