You could be right, but I would expect a player who is in line to start the season in the first team to have a properly listed number.
I'm fully expecting to see Martina play for as long as Coleman is out.
Or Everton are just making sure their first team numbers are low enough for more transfers by the time we have to register the squad to the PL and Kenny will remain in the U23's, seemingly numberless, but still eligible to be called up every single PL game.
Think people are reading too much into these shirt numbers.