The last version of the PCBs arrived, and lo and behold: they work perfectly fine! I even used the same chips and matrices that I brutally desoldered from the previous prototypes -- and they work fine too. That means I can make my order for the mass production!

Well, for some definition of mass. I have panelized the design to fit 4 boards in are of 5x5cm, to maximize the yield. A single order of 10 boards should give me 40 boards -- and that's how many I plan to make for a start, ten of every color. I have ordered the chips and the matrices already, so the PCBs will be the last component to arrive.