A fixed week owner still has to pick a check in day so yes they can
Actually, I think that is too late. Here's how I do it and I've never had issues. I start dialing the number around 8:55 am EST and keep hitting re-dial until the line picks up. I also log-on to my computer and hit refresh until the week is available. Lately, I've noticed the online part is a heck a lot faster but you can only do that for 12 month reservations. However, since online reservations have been available I've discovered at the resorts I own at they never book up. Waiohai has availability for every week next year up to this week. Now, not all check-in dates are available but there is at least one day available. So, I think, if you really want that July week and then, at 12 months you are going to have to have multiple phone lines going and the computer to try and snag a week.
I do the same with camping spots. It is the same game every where. I even discovered how unfair the game is at reserving Yosemite weeks. At least with Marriott, there are rules.
So, my question now is that can a fixed week owner reserve multiple weeks? From your post it sounds like all of July has been reserved. So, do fixed week owners get to start reserving a week earlier. Does that make sense? Because if that is the case, I don't think that is fair. I don't think Fixed week owners should be allowed to reserve multiple weeks.
Consecutive week bookings are what the 13 month rule is all about. While I am sorry Joe missed it this year, this booking practice is a terrific perk! and clearly allows us to reserve our summer. 

I can think of only one good use for a platinum calendar like that and it is if you wanted to use the resort for trading almost all the time. While there are "lesser" power weeks within the platinum season, the trade of a platinum will usually trump that of another season. But, mostly I think the best use of the elongated platinum season is the money maker it is for Marriott.