@universal soldier covered this pretty well. Here is 2 of his posts.
So it's pretty easy to test this via Google search and I do think that it will resolve itself with time. As I posted earlier, one of the main factors in getting your site indexed is the robots.txt file. As you can see here: https://www.cgccomics.com/robots.txt the old URL was blocked.
user-agent: *
disallow: /boards/*
It seems however that boards.cgccomics.com is not blocked but it does take Google time to come back and reindex your site. Eventually it will follow the Chat Boards link on the cgccomics.com navigation and results should grow. It might not be a bad idea to remove those lines from the robots file to make sure. I also am not privy to any other settings that may be in place within the site settings that would prevent this either. I don't see anything in the webpage source code that would block this.
Testing:
One of the easiest ways to see if this or any site is indexed by Google is to use "site:" when searching.
site:boards.cgccomics.com returns 1680 results including some threads from 2005. That's a positive step in the right direction.
site:cgccomics.com returns 68,100 results including many links to boards.cgccomics.com
site:cgccomics.com/boards returns 56,600 results but random sampling shows no comic related results, only coin forum threads.
Ultimately I would think keyword searches or pre-pending your keyword search with boards.cgccomics.com is the best approach for now. For instance searching for "boards.cgccomics.com moderation policy" (without the quotes) returns Matt Nelson's post from last week as the number one result.
Getting better results from just keywords will take time as you are now on Google's schedule but searching should be easier going forward. I really have no idea why this was blocked in the first place.
To back up my point if you search- boards.cgccomics.com Marvel UK Price Variants
You get the same top result for the old URL but the second one is for the new URL and it has a description. Google will sort this all out with time...