If we are talking about the same thing this is one of my biggest complaints about the amazon system. Often I will look back through my purchases and favorited items to find that they have coopted the review score for a completely unrelated product. I might understand if they were retaining page rank for a refreshed product that replaced the old one (sometimes this is the case), but not when there is absolutely no relation.
The second part of this is how variants are handled. If you are ordering, for example, a t-shirt and the options are simply different colours, it makes sense for them to share reviews. Instead you will get things like a company’s entire line of routers sharing reviews. This makes nearly all of the reviews useless to whatever you are actually looking for!