The first question to answer is if the site itself is a blog... or if it's a website that also has a blog. If it's the latter and the blog lives at www.yoursite.com/blog/, then the structure should obviously always include the /blog/.

Responding to your 3 examples in order:

Quicksprout's structure is a little odd in that their blog lives at /blog/, but the individual posts do not. A bit strange from both a human usability and bot crawling hierarchy standpoint. Other than that, including the date is helpful in terms of telling the user/bots how current the post is and differentiating it from similarly named posts on the same blog. That said, it pushes the title/topic keywords further out in the URL.

Moz uses /blog/, which again makes the most sense, but they've foregone including the date. This, however, lets them get the topic/title keywords to appear earlier in the URL.

SEO Book, like Quicksprout, oddly strips out the /blog/ directory from the URL. Other than that, their strategy is the same as Moz.

The winner here, in our opinion, seems to be Moz. The /blog/ remains when you're on individual posts which makes sense to both humans and bots. They don't include the date, but historically that's not been critical.

I have a client, a plumber, who bought another plumbing company (and that company's domain) at one point. This other company was very old and has a lot of name recognition so they created a dedicated page to this other company within their main website, and redirected the other company's old domain to that page.

This has worked fine, in that this page on the main site is now #1 when you search for the other old company's name. But for some reason the old domain comes up #2 (despite the fact that it's redirecting). Now, I could understand if the redirect had only been set up recently, but I'm reasonably sure this happened about a year ago. Could it be due to the fact that there are many sites out there still linking to that old domain?

Thanks in advance!