I doubt that they copied based on posters, they most probably created their own microphotographs after decapping the chips. The posters couldn't be detailed enough to gather more than basic structural information (which might have been enough for inspiration, but why should've they be satisfied by the snippet when they could have the whole cake?).

I have seen the pictures of i8080 chip (A0 sized photos, several of them covering the whole chip area), together with a (color) plot of the masks, based on which our local semiconductor manufacturer in the then Czechoslovakia made their "version" (MHB8080). I was too young to learn from them, but was told that the full reverse engineering process required a set of these pictures taken after each step of a series of selective etch.

The 8051 was not - ehm - reproduced here, only the 8048 (I have one piece of it in my office).

Jan Waclawek