According to Google article, the "Not selected" includes 301 redirects so it will certainly not decrease the number and I agree, in some cases may increase it.
So theoretically, if you redirect one of "not selected" URLs to existing "indexed" URL, there should be no change to the number of "Not selected".
But if you introduce new URL structure and then redirect a "not selected" URL to a new URL then if new URL ends up also being "Not selected" then "Not selected" would increase.
I am pretty certain about robots noindex pages increasing "Not selected" pot as I saw this 6 months ago when I dropped 6000 pages by noindexing them from one of sites - the "indexed" went down and "Not selected" went up in parallel - the graph was symetric.
I am also pretty certain about 404/410 reducing "Not selected" as I am in the process of sorting out the mess of 80,000 "Not selected" URLs on the site with 8000 pages indexed but with only 1500 unique pages worth indexing (huge number of duplication owing to dates in URL, capitalisation, parameters order and other classic URL mistakes). We are redirecting only about 2000 URLs and letting all others go 404/410.
The new URL structure went live last week and Google has already dropped 1K URLs from "Not Selected" count.