The source is according to me. Users booked devices in the different campaigns they didn't bought a device. They booked a ticket that can be transformed to a device if the pay the price of the device. Jolla has set an end date for this ticket. So let's say that the first one that prebooked a 100 euro other half can't won't use his ticket until last the valid day of the ticket. If jolla going to ship only 100 euro devices first, no one else can get their phones because this guy was first so he shall have the device first.

That's way I said it's more important when you do the next step than when you booked the device.

Location however might be a factor. Since some country's will probably get it faster.

As I said I can't know how many is in a delivery but as I also said, jolla said 50k is standard for a small compony.

At current state jolla had two campaigns and it's not very likely that they have sold 50000 preebokings here. How can get a conclusion like that? Well, I use campaigns like Ubuntu edge, fair phone and other pre booking campaigns. 50000 is simply to big of a number according to this.

Now, we don't now how long jolla will be waiting so they might have time for 10 more campaignps before launch than we have to analyze the possible impacts of them. They can also reserve devices for operators based on hidden deals. But from what I know operators won't reserve any real numbers form an unknown source. Must be tested on markets first.
So this is how I was thinking and if you think I was completely wrong, just share how you think the sales are going.

Also, booked device is not the same as sold device since it will be few that won't go for the final product.