Any created player you've just made will not show up until the following transfer period, whether that's the mid-season break or at the end of the season. When you "load" into Week 16 and the "pre-season, really end of season training" it will load all the players you've created into the availabile players list. So, you can create them anytime, but you have to do it before you play your last game before the break or they won't make the list. It's kind of like a registration deadline... You can change all you want, up until the cut-off day (the load into the first break week). Also, unlike all the other players, the created ones are cast in stone once you've loaded them into your ML. So you had better have the appearance and stats the way you want them before you get to the load week. You can modify them up until they are loaded in the break week. Yes, that means they will be wearing the exact same boots for the next 12 seasons. Nothing you can do, except delete and re-create.