How to tell if FTP is correct without taking anything resembling an FTP test

[OreoCookie]

I don’t think that’s correct, you are conflating a description of what FTP is with a definition. Here is a quote from Chapter 4 of Friel’s Training Bible that I assume you refer to (I only have the Kindle version, so I can’t give you a page number; emphasis mnine):

@Friel

Dr. Coggan had a simple solution. Instead of requiring a 1-hour effort, he proposed doing a 20-minute test and then subtracting 5 percent from the test results. The result would be an estimate of one’s AnT. Since it’s not an actual measure of one’s lactate or anaerobic threshold, and since it is done in a field test, he called the resulting measure a “functional threshold.” The other important products of his 20-minute test are functional threshold heart rate (FTHR) and functional threshold power (FTP).

I could similarly quote Coggan.

Both authors define FTP as a measurement (of a proxy of) AnT (anearobic threshold) in a “field test”. They distinguish between AnT and FTP because of the way they are measured, e. g. proper lactate tests in a lab vs. 20- or 8-minute steady state effort. That seems perhaps persnickety, but scientifically, it makes sense.

I think “hour power” is a just a description (as opposed to a definition) that comes from time trialists who are indeed able to hold roughly FTP for the duration of a 40k TT (although also here there is an element of pacing). Without specific training you won’t be able to hold your FTP for one hour.