For bicycles mechanical trail vs. trail doesn't really matter that much. There's some strong opinions on this that matter more at the advanced/complex geometry edge cases but for most road/gravel bikes they're interchangeable as long as you remain consistent with using either in comparison between bikes.
It's also helpful to remember that trail is a driving number that is important only in that it illuminates wheelflop - which is the more succinct measurement of how a bike will handle at the front end.
A track bike with 75° HTA, and 30mm offset fork has 60mm of trail w/15mm of wheelflop.
A road bike with 73° HTA, and 41mm offset fork has 60mm of trail but has 17mm of wheelflop. This is a large change and the two bikes would have very different handling.
Wheelflop change is % based so even a <2mm change can have large effect.
Quote:
Mechanical Trail: is the perpendicular distance from the front-wheel contact patch to the steering axis (described as positive when the axis is ahead of the contact patch).
Trail: is the distance with respect to the ground from the front-wheel contact patch to the steering axis (this is the more commonly used measurement).
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Here is a graphic I made for you, all the references I have are otherwise for motorcycles/race cars and needlessly confusing. Hopefully this is more clear.
