Thank you kindly for your answers, Rob557 and BetterRed! Much appreciated!
While I'm glad it wasn't a case of me overlooking an obvious feature of the plugin, it's sad that this is a weakness of this otherwise great plugin.
It's not always applicable to just choose a part of a sentence that doesn't have punctuation and the like, because what do you do when the only part you are 100% certain on is something that
does include them?
But thank you kindly for the tips!

Especially the idea with using variants of the typographic punctuation in the search in future. That certainly would have helped a lot if I had thought about it at the time. Unfortunately, because I tend to make sure to edit all my ebooks so that they all have plain punctuation, the few times I
do miss doing that edit, it trips me up like this.
If the plugin could be modified to ignore all typographic punctuation that would be so great! I wonder if it's doable.
BetterRed: Yeah, the viewer has that selfsame behaviour.
Thank you kindly for the link!

But I'm guessing it won't be applicable for me, since my OS is Ubuntu. And the system standard search tool in ubuntu doesn't allow for epubs to be searched anyway, hence why I am using the quality check plugin. Maybe there are other search tools that do allow for epub searching and I just haven't found them yet? Hmm...