I don't know how Penguin Random House runs their ACE/RoC imprints, and per Wikipedia RoC is just ACE in all but name, but it is possible that books published under the RoC imprint have to get farther back in line in the Penguin Random House printing schedule. The other series I follow the publishing schedule closely is Alex Verus, which is also published under the RoC imprint. Those books usually take the better part of a year to go from Jacka's submission to the editor, to the bookstore shelf, which seems to parallel Brief Cases.
Not a very strong set of data points, but I'm working from a position of relative ignorance when it comes to the publishing industry. I asked Priscilla for some input in the main discussion thread in the Books section, but haven't gotten a response yet.
P.S. And if it wasn't clear, all the other DF books appear to have been published under the ACE imprint, but Brief Cases is being published under the RoC imprint.