It's a new rule that was introduced this year. Teams can use one or two riders out of their development set up in races and vice versa. It depends on the status of the race how many (1 or 2 riders) they can use. Jumbo are doing it too with Gijs Leemreize at Provence.
I think in WT events it isn't possible, but at races of the new Pro series teams are allowed one rider per race and below that two riders filling up the ranks. They are also allowed to fill up the ranks of the development teams with pro riders if I remember correctly, same procedure basically. One or two riders depending on the level of the race. One would have to pull out the exact rules to be sure what exactly they state.
Basically the UCI probably markets this as a development tool for teams to give their development team riders some experience, but of course this is also allowing teams like Israel to dump their riders in development outfits and just call them up now and then to fill up where they need someone. Which is the case with poor Avila.
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