The exact relationship between FRC and W' is variable, and obviously depends heavily upon the duration of the efforts used to calculate the latter.

That said, if you haven't done any maximal efforts at shorter durations, it is possible that your FRC is being underestimated. In turn, mFTP might be slightly elevated. This is because, although the parameters statistically well-separated (much more so than in the critical power model, where the dependency is very high), there is still a small "teeter-totter" effect.

In any case, there is one way to find out: choose a duration or durations at which your mean maximal power is lower than predicted by the model, and give it a go. Either you won't be able to significantly improve on your performance (meaning that your estimated FRC is about right), or you'll bump up the curve significantly, resulting in a more accurate estimate of your FRC.

As for stamina, yes, you can consider it somewhat of a corollary to Hunter's fatigue profiling approach, at least as applied to lower intensities (i.e., sub-FTP) and hence longer durations. As I mentioned in the webinar the other night, though, it's more variable than the other model parameters, so don't read too much into modest changes.