I forget when the cost basis reporting requirements got firmed up but there were some point where I had options from a former employer that had gone through a couple rounds of acquisitions and when I eventually sold the shares I ended up throwing my hands up a plugged in some average cost basis that was somewhere in the ballpark and called it a day. It's all pretty automatic these days but it used to often be a real mess to try to do accurately.

Yea cost basis reporting from the broker to you is better now.

Cost basis reporting from the broker to the IRS is still blank for non-covered shares though, which leads to the other common case of "forgot a page of 1099, IRS thinks it's $0 cost basis, sends bill for $10k++, but actually you owe ~$0 if you send in the correct info".