Thanks to the very helpful response from McGill University staff, Pamela Miller and Dr. Richard Virr, Head and Curator of Manuscripts, Rare Books and Special Collections, the final piece of the puzzle of the provenance for our three Sinhalese Olas has fallen into place.
To my inquiry, Dr. Virr wrote, "Dr. Casey Wood collected hundreds of olas during his travels in the 1920s in South Asia. He was, of course primarily interested in medical texts but he also acquired many other texts as well. Dr. Casey was a generous donor to McGill and many if not most of his collection of olas is held here, however, he gave examples (usually three) of medical olas to many of the medical libraries in North America. Your example would be the result of this distribution. As far as I know, there is no list of the institutions / libraries that received olas from Dr. Wood, this would be an interesting project. A definitive study of Dr. Wood and his collecting is a subject that awaits its scholar."
So now we do not have to presume any longer. But from this discovery, another project beckons: Who will step forward and do the definitive study of Dr. Wood's travels and collecting? I would love to see a scrapbook or two from his time abroad.