I don't think minor differences are enough to keep factories safe from litigation from big gen coporations and companies. I do think the CN government keeps the factories safe, however. I believe that there would be enough compelling evidence of copyright infringment present with replicas featuring far less similarities than the reps we have access to. For some instances, even just using the name on a dial is sufficient.
Rather, the issue with flaws (in my opinion) isn't so much with certain details being executed in an incorrect manner on purpose, but rather is the inherent result of how the factories just operate when assembling such things. Typically, the parts are all from different suppliers; the factories aggregate these supplies and assemble as parts are available. So, this is why there are variations. When one batch of parts run out, they are restocked, and sometimes not always with the same parts as used prior. Also, one must factor in different factories putting these watches together as well.
In the case of 7753 based anything- I believe those were phased out due to short supply of that particular movement. There's not a lot of them in circulation in relation to other more common movements. As a result, those movements tend to be priced higher when available, thus making those watches less cost efficient to produce.