Indeed there are some report of this kind of steal of data by a Mr. H Bethe around 1940, using some experimental data reported in a conference, but not actually published, to advance on some ideas about field theory. I can not tell if Mr. Bethe or his friends had memorized the numbers or if he was allowed to take they down in paper. But, I'd suggest to conference organizers that from now, besides the usual complimentary ink and paper, they should include a disposable photo camera in the conference bag.