Hi @imaginexwp ,
I am by no means an expert, but thought I would offer a bit of what I have found in case it helps. I looked around at some other examples of Google indexing old pages, and others have said Google may continue to do this behavior for the foreseeable future. Here is the article I found most helpful, despite it being about 404 pages instead of simply old pages, there is still relevant info about the length of time you can expect Google to continue to index pages.
Also, as this post points out Google still must crawl older pages, even ones that have nofollow noindex tags on them.
A few questions to get clarity:
Are you seeing those individual map pages show up in search results, or are you just seeing them being indexed via google webmaster tools (assuming that is where you are seeing them show up as being indexed)?
How long ago did you migrate to the new site, and add the nofollow noindex tags?
Cheers,
