They can still end up in the index, just with a not that says "no description is available for this page"
I remember years ago the debate Matt Cutts asked if G should index and pointed out that other engines were indexing pages that were robots.txt blocked.. meh.
I had to setup a 301 to homepage redirect system to zap all the pages I took out... although some other engines still spider looking for those pages even though I removed them with 301s over a year ago - perhaps the spammers still have links going to them?
I started just blocking all indexing from sogu or whatever it's called and similar bots in the robots.txt and then started to look at ip / cidrs to block further after thinking they would get the hint after several months.
Hope your situation is different.
https://www.deepcrawl.com/blog/best-practice/noindex-disallo...
Specifically the part:
>Noindex (robots.txt) + Disallow: This prevents pages appearing in the index, and also prevents the pages being crawled. However, remember that no PageRank can pass through this page.