"I guess the 2 entity spinoff is a pure spinoff, and the 3 entity one is a spinoff/merger with another company. Does this make any difference with ESPP?"
In my opinion, "Yes".
It's the "sale" of stock acquired via an ESPP that creates compensation income and a tax-free spin off simply is not a sale. It would seem like the basis allocation required when a spin off occurs would apply equally to shares acquired via an ESPP. So all of the "per share" numbers on the Form 3922 would be allocated in a similar fashion.
So, logically, the spin-off of SeattleCo would result in those shares also being considered as "acquired via an ESPP" but would not generate compensation income because no sale has occurred. However the tendering of the SeattleCo shares for MicroFocus is, legally, a sale and would create any ESPP compensation income. To make that more clear, you could have immediately sold your MicroFocus shares, at no gain or loss, and converted the proceeds of your SeattleCo shares from "stock" to "cash."
