Is it better to know the truth about your book?

I can't believe it's the 17th  October already. Seems like only yesterday I did my beginning of the month post.
Over the past three weeks I've been beta reading a couple of books. One, a WW2 adventure from an American I met online and the other a literary fiction by a man I've met in person - but connected through ALLi.
I use four beta readers and don't expect more than a yay or nay from them but, as an ex-reader for the RNA wonderful NWS scheme,  I couldn't read without commenting.
Both books were good, one much better than the other. Both had technical issues and one historical errors. I sent them a one page critique listing what I'd seen and suggesting ways to put things right. I also stressed that these were my opinions and another reader might love the book as it is.
What I'm now wondering is, did they want to know there were things I didn't think worked? Should I have just said it was okay and good luck?
I had a reader contact me about typos in a book - I was so glad she did. The file published was not the final one but  an earlier version - there were indeed  many errors - but no on had mentioned this to me before. Therefore, literally, thousands of people had read the book and I so wished I'd known last year and corrected it. These weren't catastrophic mistakes, just missing letters, extra spaces, the usual things that can be overlooked if not correctly proof read.
I have contacted a few writer friends over the years to tell them that there's a historical error in their books - all have been pleased to know. One famously said that the book was only £0.99, and what do readers want for that money? This reader wants historical accuracy whatever the cover price.
I always correct the e-version of the book if I discover/am told about errors but don't do the paperbacks. It costs £100 to have it formatted and I only sell a handful of copies a year.
Christian Cameron's brilliant book, The Long Sword, had so many errors I stopped counting them after three chapters This was the hard back. The unproofed file had inadvertently been published. I was reviewing it for HNS so contacted Orion and they said they would make sure the e-version and paperback were correct.
I think most writers would want to be told before the book was published but what about afterwards when they could do little about it? I never read my books again once they are 'out' and I doubt that many writers do.  So why tell them as they might remain in blissful ignorance until a reviewer comments?
What do you think? Tell the truth or not?

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