I agree with Toshi one hundred percent. It's strongly recommended to change it. I'd say it's crucial you do it. There's absolutely no reason to not do it.

Great question Dan. @Jesse, you are on the right track. I think the question was misunderstood.

The question is, if seomoz.org links to Amazon.com/nakulgoyal and that page does not exist, is there link juice flow ? Think about it. It's like thinking about a citation. If seomoz.org mentions amazon.com/nakulgoyal, but does not actually have the hyperlink, is there citation flow.

So my question to the folks is, is there citation flow ? In my opinion, the answer is yes. There's some DA that will get passed along. Eventually, the site owner might identify the 404, "which they should" and setup a 301 redirect from Amazon.com/nakulgoyal to whatever pages makes most sense for the user, in which case there will be a proper link juice flow.

So to clarify what I said:

• Scenario 1:
  SiteA.com links to SiteB.com/urldoesnotexist - There is some (maybe close to negligible) domain authority flow. from siteA.com to siteB.com (Sort of like a link citation). There may not be a proper link juice flow, because the link is broken.

• Scenario 2:
  SiteA.com links to SiteB.com/urldoesnotexist and this URL is 301 redirected SiteB.com/urlexists - In this case, there is both a authority flow and a link juice flow from SiteA.com to SiteB.com/urlexists

**That's my opinion. Think about it, the 301 redirect from /urldoesnotexist to /urlexists might get added 1 year from now and might be mistakenly removed at some point temporarily. There's going to be an affect in both cases. So in my opinion, the crux is, watch your 404's and redirect them when you and when it makes sense for the user. That way you have a good user experience and you can have the link juice flow where it should. **

Taylor, you are 100% on the right track. All the answers exist in your question.

#1. These are "redirect notices", not errors. More like warnings.
#2. As long as they are canonicalized correctly, which you said "do I need to do anything if both those pages are canonical to the parent product".

There's absolutely nothing you need to do. You are good. It's always good and important to verify these technical SEO issues. I hope this helps.

I think that's a little too much. Slow down. Revisit your link profile. Do a complete audit for yourself and the competition. See what you really need. Revisit your On-page and then fill the gaps. That's a little too many unless you are talking about an authority site/brand with considerable customer base, traffic, audience to justify this as natural. Are these all same kinds of links/citations ? Blogs/Blog comments/articles/press releases/guest posts etc etc ?

As long as you are not over doing any one specific kind of link building, I won't worry. A good mix is natural. Don't bother too much if there are certain citations, follow, nofollow. It's the normal nature of the web.

As Chris said, How many citations are you adding in what period of time?