...and make me feel better. I just did it. I was absentmindedly lightly cleaning a Duco pioneer with a damp cloth. I said to myself "stay away from the date stamp" and then promptly flicked over it with the cloth - gone, just like that. I'm still really annoyed with myself.
For the record, the date was 21 May 1963 and you can only make out very faint traces of it now. Idiot!