Congratulations on your new bag!
I talked to customer service about the availability of a different product earlier this week, and she said, "Let me look at the production schedule...." My impression (and it only makes sense) was that they have a schedule of which products they're making next, and then after that, and so on. Since your bag just went out of stock, it seems reasonable that it just hasn't made it back into the queue yet, especially when there are a number other products and color combinations that have been out of stock for awhile.
Of course, I'm just making a guess, but it seems likely that the Navy and Northwest Sky A45 will find its way back into production at some point.