From A Day by Day Chronology of Mr. Sherlock Holmes according to Zeisler and Christ by William S Dorn:
May 20, 1900, was Beppo’s last pay day at Gelder & Co. [SIXN]
“No, no,” cried Holmes, “not a word to the cousin – not a word, I beg you. The matter is very important, and the farther I go with it the more important it seems to grow. When you referred in your ledger to the sale of those casts I observed that the date was June 3rd of last year. Could you give me the date when Beppo was arrested?”
“I could tell you roughly by the pay-list,” the manager answered. “Yes,” he continued, after some turning over of pages, “he was paid last on May 20th.”