You are trying to put an exact number something that is impossible to put an exact number on.
You're right—JWs probably don't have an exact number either, but I’m willing to bet that their margin of error is smaller than what historians have to work with.
One of the reasons I spent so much time looking into these numbers is that I was raised as a JW and repeatedly told that had I lived in Germany at that time, I would have been sent to jail and likely faced execution. And, as you seem to believe, I was told this story to reinforce the idea that JWs were the true religion because of their persecution.
However, the numbers show that the majority of JWs weren't incarcerated, and only a fraction were executed. While this doesn't diminish the heroism of those who were (in my book, they're heroes), it is a disappointment compared to what I was led to believe when I attended meetings.
JWs were an “island of spiritual resistance” and that other churches have had to come to terms with the “widespread complicity” of their leadership and ordinary members
While this statement is true, "spiritual resistance" was not what the Nazis needed at the time. As I said before, martyrdom didn’t win the war—physical resistance did.
any act of resistance was remarkable in the circumstances
That's where you and I agree. However, Jehovah's Witnesses don’t share this view. They don't believe in physical violence. In their view, those who picked up a gun to fight the Nazis were enemies of God. While the Nazis were killing millions, JWs were preaching that God would soon bring about Armageddon and kill exponentially more people who didn’t share their beliefs. Jews, Catholics, Protestants, Muslims, Hindus, Buddhists, etc., would all be destroyed.
Essentially, they didn’t see resisting the Nazis as a way to serve the greater good of humanity. Now, nearly 100 years later, history shows that humanity needed Catholics, Protestants, and Muslims to pick up arms and fight back because God remained idle and did nothing.
Someone who spoke against the regime, went to jail, renounced their faith in custody, was released, later regretted that decision and rejoined. Did they resist, or not?
You enumerated several scenarios in which people could have renounced their faith, even temporarily, in the face of persecution. I completely agree with you there. I'm not in a position to judge them from the comfort and safety of my home. I probably would have been the first to sign the paper and say, “Heil Hitler.” But I’d like to think I wouldn’t have given up names, that I would have helped people evade the Nazis, and that I might have blown up some train tracks.
The point is that the same can be said of millions of Catholics and Protestants who faced similar choices. Was their faith worth any less than that of Jehovah's Witnesses?
Someone who was a JW for social or family reasons but decided it wasn’t worth it when the Nazis came to power.
The same can be said for other religions. You also have to consider that, in Germany at the time, you were either Catholic or Protestant. But how many of them truly believed and practiced their faith? Those who did often lied to the Nazis and fought clandestinely.
All this to say that the JWs response to the Nazis didn't make them the true religion. It was one way to face it, but it didn't make them the one and true religion.