Page 6 in the bottom left corner of the first panel looks significant, I haven't read any other works by Masuda Eiji besides Jitsu wa Watashi wa
Page 9 first panel has the wolf girl and the crossdressing alien
Page 13 second panel looks familiar, idk though
Page 16 third panel has Glasses girl and alien girl
Page 17 first panel, is that shiragami's dad? I didn't recognize I thought it was a diff character
you missed Shimada on page 3
page 6 on the bottom left are from
Yumemi Ga Oka Wonderland and their names are Kotauro and Akogi
I think on page 9 Genjirou from Jwww is supposed to be in that panel too in his "Ryoukuenzaka Yumi" disguise, and the comment you are replying to also assumes so I imagine because don't see anyone else resembling Genjirou in his disguise or spot Touko anywhere
page 13 on the second panel has Hachi, Handa and Inohara from
Weekly Shonen Hachi and I am little disappointed Mike wasn't there lol
page 17 is either Kurea from
Yumemi Ga Oka Wonderland or Miki from
How to Make an Invisible Person but I can't decide quite which one, their designs are pretty similar and here it seems almost like they got mixed; Miki has white hair but she has a very distinct attire, while this cameo character has clothes that are closer to what Kurea always wears.
I recommend reading Masuda's other works, I'd say none reach Jwww but they are pretty good, and
Yumemi Ga Oka Wonderland is also a cameo fest, so I'd say read it after reading Masuda's previous works to catch them (and also there's cameos from
Sakura Discord in Jwww here and there that you may have missed, and a reread of Jwww is always recommended in my book)