Highly doubtful... I really think that is just to be expected with this lens design. There will be slight copy variation lens to lens, no doubt... But distortion is generally not one of those variations.
What is being made now is most likely what is being made years from now... Very very small changes in production, possibly. But they would not release sub-par products early on, that is just silly and stupid for a company to do. Imagine if that was the case? Canon can get a TERRIBLE bad reputation extremely quickly if found out.
The delays in product are just normal. Maybe they had other priorities on the product lines (5D3, 1DX, super-tele's, etc...) before they switched over to the 24-70 and had to make upgrades to robotic equipment to produce the lenses or something of the sort. I don't think it will have to do with actual changes to the lens, just the methods to build the lens. Just like some car manufacturers, they must upgrade production and assembly lines for new car models. Canon probably had to do the same. The delays could simply be just due to this reason and nothing at all with the lens design. Everybody assumes it has to do with the design or final tweaks to the lens itself but I honestly think it was final tweaks to the production equipment more than anything. Most likely once that was figured out, they tested with test lenses and made sure production was outputting ideal lenses to spec. Once that was complete, they start mass production which we will have in our hands once orders get filled.
I would not think much into it though... This lens is finalized and complete. Production is running and I am sure a few containers on ships and planes are currently en-route to the US and other countries to start fulfilling demand. I don't think the lens itself will change internally at all, unless a fault is discovered and most likely be "recalled" and repaired at local facilities if your lens is apart of that said batch.
I wouldn't worry about early copies, though. Canon does not tend to have issues like Tamron with elements falling out