It really depends on the business you are talking about and what their conversion model looks like…. but in chatting with someone trying to model your works value within an org….
If private equity is involved and looking to build models, then I would assume that this business is engaged with multiple marketing channels aside from PPC and organic search.
In those situations I find it is helpful to zoom out and place SEO within that context.
On the range of TV ads, Billboards, Influencer marketing, traditional PR, radio ads, corporate sponsorships etc. etc. and paid search (which can give you a pretty clear CPA) - SEO is sitting somewhere in the middle with regards to how easily it can be measured.
The later have been around for _significantly_ longer than paid search and SEO.
In my experience, the more “traditional” marketing streams are still able to be factored into models. And have been for a long long long time.
So i’d zoom out, ask your model person “How would you account for/model for, say, the tv ads we run? What data do you use there?”
And work backwards from there.
No doubt you will have way more data than that department does, so the model can be more accurate.
And since it is working off the equity persons existing model, but you are making it more accurate,. they should be pretty satisfied.