PCB codes/dates written on them aren't a perfect source of infos. Sometimes PCB are reused between releases and the writings on them aren't updated. Overall they give you an idea of when they could have been released. There are only a handful publishers that actually cared for "precises" dates.
There is pretty much no way to find it out exactly unless you find advertisement for an upcoming release (Sachen did a few, for example), a compile timestamp in the code or like a timestamp that was sticked to the cartridge back when it hit the market (which is super unlikely).
