> If you have a proof of concept, have put in some thinking, made UI sketches and flows, etc, you have started building the product,

I think that that bar is too low to move from "we're considering building $FOO" to "we're building $FOO".

I mean, with the bar for "we're building $FOO" being "Investigate demand for $FOO", then the phrase "we're building $FOO" loses all meaning.

It's the difference between "we're getting divorced" vs "we're considering divorce".

"we're starting a new job" vs "we're looking for a new job"

"we're building a LEGO deathstar" vs "we're buying a box of LEGO"

I see no reason that "we're determining whether to build $FOO" is the same as "we're building $FOO"