However I would wonder, "well if there is this mistake in one book, how many more are there in the whole series? I've bought the lot...they are likely to be purchased by libraries for their large print section".
A vague memory crossed my mind so I checked it out,
"Does the British Library have a copy of every book published?
Legal deposit requires publishers to provide a copy of every work they publish in the UK to the British Library. It's existed in English law since 1662. Since 2013, legal deposit regulations have expanded to include digital as well as print publications.
Even if a book boffin there wasn't directly interested, they may point the way as for what if anything you can do?
I tried contacting various people and in the end contacted the RNIB as they have a library which includes large printed books and I hope they take this matter up as not all of the people who read large print books are old they can also be teenagers with poor sight and maybe doing exams.
Yes, just a typo, but irritating! I was given, some years ago, a recipe book, which I discovered had a typo. Double the amount of butter in a cake recipe, so pretty annoying. It was a cookbook from a food company, so I contacted them. They thanked me and sent a big box of goodies. But to my certain knowledge ( because I checked every time I saw a copy in a shop) they never even put in an erratum slip!