What date to use after years of mergers splits and spin offs!

I show non covered capital gains from a stock that I originally purchased in 2001.

Here is the history:

2001 purchased shares in compaQ

2002 HWL bought Q became HPQ

2015 HPQ spun off HPE (then HPQ name change to HP)

2017 HPE spun off DXC

2017 HPE spun off 2 step seattle spin co / micro focus

2021 DXC spun of Perspecta - 

2021 Perspecta = private company my 1099B shows in with no cost basis.

I have done all the figuring I can do do arrive at a cost basis after each corporate action for each stock.

Thought I was done.... but the Acquisition date is stumping me. 

In my mind, it cannot be - as it was not - "various", it seems that it would either be the ORIGINAL purchase date, 

or the last spin off date. (which would have been covered and listed as 0 as it was after 2011)

If anyone has the exact IRS code for this I would love to see that! 

HP Alumni website was invaluable, but I don't recall anything about what acquisition date to use!

Thank you Thank you!