I was prompted by YBF's comment on how rare Komusubi Yusho were to search up all of them. It turns out that in the 6-basho era, every single Komusubi Yusho winner had it as their either 1st or 2nd basho in an Ozeki run. Just before the 6-basho era, in 1957, there was one failure, Annenyama (later known as Haguroyama). If you remove all the date restrictions there was another failure in 1932, but he might have made it eventually if he hadn't passed away a couple basho later (Okitsuumi). There were only two other Komusubi Yusho, so the pre-6-basho era had 2 failures and 2 successes, not much of a pattern compared to the 6-basho era ones.
Also of note is that Musashiyama was promoted to Ozeki directly from Komusubi after the next tournament, and that wasn't even the last time that happened with the more recent one being even more ludicrous by today's standards with only 1 sanyaku basho, so clearly the rules were different when there were less basho per year.