Sounds like a horrible way to me. Instead of just saying "For now we are starting with the options from the 2014 PHB and here they are in this document" is a lot easier than saying, Hey, we are using stuff from all over the place, but only a little bit of it and here is the document." Because the next question that would rightfully be asked is "Well, what about this Boom Stick class from here? Or the Van Helsing class from there?" Sticking to the "official" book to start with is much easier to justify than a curated list of seemingly randomly selected classes.