This is OT but books can vary in quality too - specifically the paper used and the print quality. I was looking at "Physically Based Rendering" (http://a.co/bL8bjUw) after seeing the post here about rendering a scene from Moana and was disappointed to see comments about bad print quality. Hopefully this is fixed in a later print run.

>Also if Batch C is being sold or something similar (to batches), a better idea would be (IMO) to have the product owner comment on the review, saying we have fixed this in batch 2 or batch B or something

That is a good idea, but that still does not fix the aggregate data. When someone searches for "Coffee", the aggregate number of reviews is still considering that low-star review. So the "Seattle Coffee Beans" overall rating for Batch C could be a 4.5 / 5, but for all batches is a 2.5 / 5.

The easiest way to fix this is to remove old, out-of-date reviews. This should apply to positive reviews too, but I have no idea if Amazon is doing this.

Another approach is what Steam did - have a long-term rating and a "recent" rating. See "No Man's Sky" as an example [1] - a product that started poor, but improved over time. This helps prevent product brigading and gives vendors an opportunity to bounce back from negative reviews.

[1] https://store.steampowered.com/app/275850/No_Mans_Sky/

Not necessarily. The album Pinkerton by Weezer was critically panned at release but now regarded as perhaps their best album.

Tastes change. That said, you can still find those old reviews. Not so in all cases on Amazon...