Well, I myself can't tell you why those pages would have errors - I don't know your site to know what is right/wrong or what your folder structure needs to be to ensure the path is correct. Or, as things that have happened to me, for example, in Google Webmaster tools, I'll get notification for 404's to my site pages...even though those pages don't exist. What do I mean? I mean someone linked to my site, but messed up the URL so they (unintentionally) created a bad URL that Google associated with my site. So when you say you have a high amount of errors/warnings, I'd just suggest looking at what  tool is providing that information to determine how credible that is.

As for those URLs you shared, are all those legit pages but aren't rendering correctly? Or, are they not real pages at all but somehow the URL was created in the move? (Someone else may be better at chiming in there other than myself.)

I suggest going back and redirecting all the bad pages to a good page, or serve up your 404 page for any bad links you want to fall out.

Even with errors, sites can do better with traffic if the migration means that the site is more crawlable and that along with the migration, if it's easier for search engines to figure out what your site is about and match it to search queries.

Wondering if you can give a bit more background -  so did the migration change your URLs/URL structure? If so, what was your link plan to set up redirects from the old URLs to the new ones? Did you update your site map to indicate to the search engines you've migrated? Did you 404 any old content that you weren't moving?

As for your comment "Few are mentioning sites I never seen before on the Yahoo! platform" I'm not sure what you mean - what sites are you referring to? Yours? Sites that were linking to your old site...?

)

I had it happen in a sitemap I submitted to Google in my Webmaster tools and it didn't like it. So I removed it and resubmitted it.

Personally, I don't go by score. I go by content and what's best for the user and what's most "matched" or "alike" so it reads naturally. My intention isn't to sound smug, but when writing content, I can tell when it's stilted and the same word is used over and over (both my reading and doing a count of it) vs using variations of it. Also, there's tools that I use to at least get an indication if Google might think something's up (i.e., not diverse enough).

Also, my site isn't about one topic - we have a few core things, but we sell more than 30,000 SKUs so it's easier to be more diverse, even if there are similar variations (arc flash labels, cable labels, etc.) which makes it easier.

I track my site/words in a spreadsheet so I can make sure we're not optimizing the pages for the same words and competing against ourselves.

As for backlinks, that can get a bit trickier because I have less control on how people select to link to our site. For that, I monitor and when I feel it's needed, make suggestions and/or collaborate with other sites. (Keep in mind I have 50,000+ pages.)

It's all of those. Those are all ways you seem too fake and "perfect" and it flags Google. Similar phrases (ex: labels, labeling, labeling printers, identification labels, etc.) are all more natural variations of each other that hit home the essential core message (we're know labels!) in a more natural way than having just the word "label" everywhere.