Michael notes in a comment:
Although Ball received letters from the riders' national federations of Colombia, USA and Spain confirming that the three riders were not involved in any open investigations, Messick clarified by stating the UCI's direct confirmation was enough to exclude the riders from starting. "The letters are irrelevant, and whether the athlete is eligible to race in UCI races has no bearing on what all seventeen teams agreed to about the eligibility of riders for this race. Every team agreed that no riders who were under an open investigation would participate; it's different from UCI eligibility. Every team agreed the UCI and USA Cycling would tell us about any riders who are currently under investigation and that is the criterion and the basis – that's the rule."
It appears to us this "confirmation from the UCI" showed up after the press conference, and before the Rock team meeting reported by Ruibal.
We wonder how planned this was. The late timing makes it difficult to refute, and it seems magically pulled out of the hat just as Rock appeared to be willing to to press the point.
The general technique offers quite the escape route for all sorts of interesting behavior. Now, to exclude riders, all that appears necessary is for promoters to add an "open file" rule, and get a fax the night before a start to axe anyone they don't like. No due process, no recourse. It reminds us of the USADA "we'll test the B's anyway" gambit, hinting at the influence of Richard Young. Whatever you thought the rules were, they aren't.