Only about as often as most other people.
If/When I do, I'd probably say; "Sorry, I made a mistake there." I'd correct it. I'm sure we'd all think no more of it, if no harm had been done.
Suggesting putting a 3-port alone on an unvented water heater is inadvisable, as suggesting putting a 2-pin plug in a 3 pin socket or using a wad of kitchen foil to replace a fuse is inadvisable. It may work, under non-fault conditions, but it's really not to be recommended and it shouldn't stand uncorrected. Other people trying to defend or justify it just suggests that they don't know much about the subject either.
Whilst you may question my technical abilities, it seems that I may know a little more about unvented water heaters than some here. Nor do I assume that I have know all the answers; I cheerfully admit to knowing nearly zilch about computing or Usenet and many other things. Most other things, even. Usenet I will probably look into, but I have more pressing problems at present; something else for the 'must do' list. I hope that I know a bit about pipes and pumps and stuff like that, but I am here in the hope of learning from those who know more. My first post in this thread was then about the 66th, of which about
12 were on-topic. I don't think I'll be learning much here.