Yep, I ran into this too. Technically my 1099-B "date acquired" isn't blank, it's N/A. I guess a couple of the stocks in my investments did a reverse split so I had a few "cash in lieu" entries with no cost basis and no date acquired.
The "learn more" link brings up a help page with the following text:
"If you don't have a single date listed in Box 1b of your 1099-B, you can select Something other than a date. After you select this, you can choose from two options: Blank or Various (or more than one date)."
Choosing "Blank" earlier on was fine, but at the end when it's checking for issues, it then goes back and refuses to accept "Blank". Maybe there were some other scenarios where Blank would have been valid? Otherwise they should just force you to pick Various.
Various does seem to make sense for me, because looking at the transaction history on my investment web site, it looks like they bought shares of this stock at various times over the years. It doesn't seem possible to find a cost basis to enter, if it was bought at various prices at various times, so I'm leaving that as 0... Luckily the proceeds are pretty small since it seems like they're only what would have otherwise been fractional shares.
