Oh man, you only have info from 2012 on?
Good luck! Hope it’s easier than you think and that you don’t have to declare $0 cost basis.
I have records going back 30 years, but I don't think the Mutual funds providers were required to keep records until 2012.
I'll do a search to see exactly what the 2012 ruling is.
EDIT to post the results of my search.
"Brokers are only required to keep a record of your stock shares purchased after January 1, 2011. Cost and holding period for mutual fund shares are only tracked for purchases after January 1, 2012. Brokerage firms start maintaining details about bonds and options acquired in accounts after January 1, 2014. Consequently, a broker or mutual fund company may have a record of cost for some recently purchased shares but not older shares in your account."
From:
https://finance.zacks.com/covered-vs-uncovered-shares-10752.html Several other sites show the same information.
Next I'll contact Vanguard to see what records they have and how far they go back, even though they weren't required to. I'm disappointed they aren't open weekends, but that's why I'm only charged 0.04% on my VTSAX. :-)