Universal Toy & Novelty Co. printed a variety of 10-card strips in the 1919-21 era that include these W529-1 boxers. Note the title text on the middle cards of their strip; all 1919-21 Universal boxing strips appear to be W529-1s.
Seven of these arrived this week, cutting my needs to #6 Fulton and #9 Dempsey. Fingers crossed I can finish it off this year.