Sorry, rjm33, but the reality is that "Responders" to altitude training don't show an increase in the level of Hct and Hb, but instead are able to increase the ability to catch more oxygen from the atmosphere.
And this is due to the INCREASE of affinity between Hb and O2.
The researches you are speaking about, that you can find in the physiology textbooks, are not referred to people having some hard activity, but to people simply STAYING in altitude.
When you, because your activity, need more oxygen, the body learns how and where to look for having more material, in this way increasing the ability to take this gas from the atmosphere. This is what happens in athletes "responders", and is what doesn't happen in "not responders", who follow the trend explained in your textbooks of physiology.
I had, in 2014, a clear proof of this. I was for two following months in a training camp in altitude (Duoba, 2400m) in China with 22 athletes, preparing Asian Games, and I could use a very good lab which is among the facilities of the Center, for weekly blood tests with all the athletes of the Team. This because, for the first time, I had the opportunity to follow the development of the blood values step by step, not only with tests before going to altitude, then immediately going back sea level.
The results were very interesting. Many of them had a good percentage of enhancement of their values, specifically Hct and Hb, but some of them didn't show any real change in the most part of the tests we did.
Who were the "responders" ? The one not showing any change, since they improved dramatically during Asian Games, moving from 2'07" to 1'59"48 in 800m (Zhao Jing), from 15'55" to 31'53" and 15'12" (Ding Changqin), and from 9'57" to 9'35" in steeple (Li Zhenzhu). ALL THIS ATHLETES COMPETED WITH VALUES LOWER THAN BEFORE GOING ALTITUDE.
At the same time, several other athletes showed a clear increase in the values of Hct and Hb, AND NOBODY OF THEM WAS ABLE TO IMPROVE THE PERSONAL BEST (not responders).
People must put in their mind that the reason because we go altitude is to put the basis for running faster, not for increasing Hct or Hb.
It's a FALSE SUPPOSITION that the results of middle and long distances depends on the level of Hct and Hb. These are the EFFECT of training, not the CAUSE of performances.
So, if athletes can run faster without changing their values, which is the reason ? Is the increase in the AFFINITY between Hb and Oxygen, that happens only for some athletes (the "responders"), but is due to the proper training they can do IN THOSE SPECIFIC CONDITIONS.
About other changes (for example, larger, stronger heart), you clearly understand this doesn't happen because of training in altitude, but because PROPER TRAINING FOR ENDURANCE in any condition, including sea level. So, this change (which needs long periods of training, about 6 years, so it's not something that can change quickly) doesn't have any root in altitude training.
You say that "The most important effect of EPO is on the number of RBCs, not the size of RBCs (MCV or mean corpuscular volume)".
Again, there is a misunderstanding, between REACTION of athletes going to a new condition (coming from sea level), and ADAPTATION of athletes living and training in that normal condition. I can assure you that, in the second case, THERE IS NO INCREASE IN THE NUMBER OF RBCs, BUT IN THE SIZE OF RBCs (MCV).
The problem is that all the text books of physiology speak about differences from sea level and altitude using as subjects sea level persons, and not top athletes from altitude.
So, it's not true that "textbooks and findings of science are INVALID for your claimed separate human species of athletes for whom the physiology textbooks do not apply", but that are INVALID for ALL PEOPLE LIVING IN ALTITUDE, WHO HAVE ADAPTATION AND NOT REACTION TO NEW SITUATIONS.