Imperfections in Nature are mostly assymetrical. Perfection tends more to be symetrical (snowflakes for instance).

This imperfection on Yoda's back looks even more natural being assymetrical... To my eyes.

I agree. Yoda doesn't have to be ''perfect''.

In fact, I haven't even noticed these little ''bugs'' you are talking about in these 857 pages. Only lightsabers and laser bolts have bothered me and I couldn't understand why Lucas didn't redo them. But anyway, I really appreciate your job, Ady ;)