Okay, I don't bother to note when I've fixed a typo or added a missing word. Those don't usually affect the meaning of a post in a material way.
I did write one significant silent correction, where a friend quite rightly emailed me to say I'd been unnecessarily nasty to someone. The edited post was a lot better than the initial version.
Yesterday, I found an error on a blog I've been reading for a couple of years: a photo caption that incorrectly identified a street visible in the photo. I wrote a polite comment noting that street X was actually street Y, and that street X was not visible in the photo.
The author removed the photo, didn't publish the comment, and didn't acknowledge me or note the change. Oh, well! Not how I would have handled it, but it's not my blog, either. I wonder how many unpublished comments are out there. At least the author acknowledges on the blog that comments might be edited, which has happened with me.