I had never seen that before the West Ham Game (didnt go to Wakering), but usually teams put them in straight numbered shirts 1 to what ever not squad numbers when they haven’t been announced From what I have seen in the past.Won’t be numbers as they haven’t been announced yet. Think that’s standard practice but might be wrong
It is actually against the rules of the game not to have numbers on your shirts, i didnt know this till last season when my Sunday team got a fine for the exact same thing in our first game of the season (kit was late arriving)