Here's what Markus had to say regarding this for anyone interested. It seems Shigenori's origin still needs further research.
Thanks Markus for taking the time and effort! Truly a helpful and knowledgeable resource in the Nihonto world.
"the entry of Wake Shigenori being a student of Saburo Kunimune goes back to the Tosho Zenshu, whose info I added in full to my swordsmiths index. But I was already suspicious about that and so I added the supplement "it is said that he came from..." Now Fujishiro does not list Shigenori and the Toko Taikan does not say anything about his affiliation and master. The NBTHK says in their Juyo descriptions that when it comes to Wake, Shigenori and Shigesuke have to be named and that both worked at about the same time. They neither draw the connection to Kokubunji nor to Kunimune and just say that there is the theory that the Wake smiths derived from the Ko-Bizen group. However, they also say that their workmanship is rather close to contemporary Osafune at first glance. Well, Fujishiro was the one who associated Shigesuke with the Kokubunji School but seeing the hesitation of the NBTHK saying anything in that direction, I would say that we can't really say for sure what connection the Wake smiths had with their Bizen colleagues."