oh… you want both columns to be user-facing…
my suggestion then would be do an automation where trigger “Row changed” when Complete checkbox is checked, then check Owned for each part.
I’ve never played with SwitchIf statements before so unsure how this may help.
btw, your doc is awesome!! brings back so many memories and nostalgia for me 
and how amazing is it that coda is used for all sorts of things in lives of the people!!
Turtle Power!
MELangelo
p.s. @Rickard_Abraham suggestion above is so cool!
but just a note for those in future looking to incorporate it i.e. building implications -
as per @Paul_Danyliuk - try to limit row buttons as much as possible as it affects doc performance