Lovely day for a stout

Some time ago a colleague, checking a text I had written, spotted a spelling mistake in a passage in which I had referred to an advertising slogan: Guiness is good for you. The colleague pointed out the Guinness is spelt with double <n>. On the following day, I bought him a couple of bottles of Guinness. This is one of the few memorable instances where correction had both immediate and lasting effect: I have never misspelt Guinness since, and I think I never will. Then, the other day, rereading Heinrich Böll’s Irisches Tagebuch, I came upon a passage (p. 102) where another Guinness slogan is referred to: A lovely day for a Guiness. It contained exactly the same spelling mistake. Nobody had noticed. Böll and his editors, however, had a much better excuse for making this mistake: at the time of writing, Guinness was much less well known in this country than it is now.