A few days ago I changed the "default collection to display" on my site and, making blog #12 (Photo A Day) the default, replacing blog #2 (Mark's Blog). Later I saw a link on google to a post in blog #2 and clicked on the link. This brought me a 404 error. When I changed the default collection back to #2, the link to blog #2 from google search results started working correctly.
Looking into this I see the following:
With Blog #12 single post urls are in this format, whether it is the default collection or not:
Google had indexed the URL for blog #2 without the collection name, so once Blog #2 ceased to be the default collection googles link was broken.
Looking at the Collections / SEO tab under _Single Post Pages / "Permalink" Pages_ the permalink scheme is set to "Use extra-path:post title." The example given changes for blog #2 - and only blog #2 - depending on whether it is the default collection to display.
The permalink scheme does not change if blog #12 is set to be the default collection to display. It remains