I sometimes find that posters get a bit snarky if someone misunderstands a post or has a tidbit of information wrong. I see statements like, "I already said,", "I already mentioned", 'Again, I said that already", etc.
It sounds snarky to me. Many read threads on their mobile device, sometimes I get interrupted reading and come back later. Sometimes a thread is very long and it is impossible to remember who posted what or pertinent details.
I think if someone gets a small detail wrong in a post, is slightly confused or repeats a suggestion, rather than using a condescending tone, wouldn't it be more proper on an etiquette site to politely correct rather than emphasizing the poster had a small tidbit of info wrong or mixed up by using a tone that sounds like they are rolling their eyes or sighing that it has already been mentioned?