Actually, that's the entire point. If people didn't find out that the system was wrong until after the primary, that proves it was the voter's fault for not keeping themselves informed.
Individual citizens have a responsibility to keep themselves informed. I do not believe for a moment that the August 2015 change in rules was never reported, or that the Colorado papers or media never mentioned the March 1 caucuses. If people really care, then turn off Wheel of Fortune for a few minutes, or skip the bar one night, or give up one afternoon of fishing, and figure out how/when you are supposed to vote. This clown didn't show up at the caucuses. Why not? Didn't see anyone asking that question, or him answering, but that's really the key question in this whole thing.
Why didn't Trump's campaign run a couple of ads prior to March 1 reminding his supporters to show up? Why didn't they have delegates sheets? Why didn't they do a better job of getting people organized? That's why "when they found out" is really all you need to know. If they didn't found out about this system until after the fact, then it was the Trump campaign in Colorado that failed.
I have zero sympathy for people who didn't bother to read the rules, and so screwed themselves. Zero.
Not really.
You don’t know that vote fraud has taken place until the day of the voting at a minimum. Sometimes afterwards when certain of facts are either thought about or brought to light.
It is okay at times to claim, as you have, that it should have been known. Perhaps it should have. I’m not a Coloradan, so the normal process isn’t known to me. I’d have a really good feel for it in Ohio.
It would be instructive to see how the last 3 or 4 Colorado republican primaries have been conducted.
If this one was substantially different, and if that change had been enacted by a small group of people in leadership positions, then I think it is fair to charge them with voter disenfranchisement.