To make it simple...In Tilly's January, 1926 tri-fold advertisement, Tilly listed the "Kingston Golf Club in Kingston, New York" under "Nine Hole Courses" that he designed. The nine-hole course of the Twaalfskill Club in Kingston, New York, was originally designed in 1902 by "someone" hired by the Kingston Golf Club shortly before they disbanded as a club. Twaaflskill inherited both their members who wished to join and Kingston's financial responsibilities, which included the newly-leased property on which the newly-designed course was being built. This would now be used new site and golf course for the Twaalfskill club. Between that date, and January 1926, there was never another Kingston Golf Club organized. This means that Tilly must have designed the 1902 course.
Bret, Tilly regularly played courses throughout New York State all the way up to the Lake Placid area from the latter part of the 1890s through the first decade of the 20th century. He was well-known both as an exceptional player for his time and also as a person who both studied golf course architecture as well as put into practice both his original ideas and similar hole types used on other courses if he believed the land he was designing for was best suited for a hole of that type. As for coming up with his templates after Macdonald, one needs only look at the original Shawnee CC course to appreciate that isn't correct. The twisting of the fairways, the tees not being simple squares but of various shapes and sizes as well as parallel tees well apart from each other for the same hole along with other types of features that he would incorporate throughout his entire career; all were used at Shawnee. But he also used template holes and features at Shawnee that he brought back from his own 1895-1901 travels to the U.K. There was the famous "punchbowl" green, the "Alps" he created for the 13th hole, and one that he took tremendous pride in, were his use of "Mid-Surrey mounding" there as well.
The belief that Tilly could not have designed Kingston in 1902 is based more on the decades-long accepted belief that Shawnee was his first design. That is why it is difficult for most to accept that he had designed courses before Shawnee. Yet I have never seen a single reference that ever stated that Shawnee was the first course designed by Tilly while he was alive; not a single one. Tilly, though, on a number of occasions, was quoted in the early 1930's as saying that he began designing courses 30 years before which would have included Kingston in 1902.
As for his lack of designing other courses between 1903 & 1912, he redesigned Belfield in 1906 of which he was both a founding member and on the club's board from at least as early as 1905; also, Bedford Springs in 1910, and several others that I am still working on including one that is trying to convince me that he designed their course in 1909. The reason why he didn't design many courses between 1898 (when he designed and built the "rudimentary golf course" during the summer in Frankford Park), is a simple one. He was convinced that he was among the very best players in the U.S. and spent an incredible amount of time playing in as many tournaments as he could while still working for his father's rubber goods company. Also, he began writing for golf magazines and newspapers during these early years as well. It would be a combination of his playing successes and articles about golf courses that would lead to his being sought out to design courses.
Why do we know of so few during that time? There are of any number of reasons including the numerous clubhouses that burnt to the ground in the first several decades of the 20th century taking all of their historical and club information to the fire; that clubs simply didn't consider who designed their golf courses in those years to be of any real importance; or that a number of courses he did design are no longer in existence for financial reasons.