Deshojo is a named variety of Japanese maple. You name a variety when it has interesting features that are worth preserving through asexual reproduction, i.e. not seed.
Asexual reproduction include: cutting, airlayer.
If you plant a seed from a named variety that produces seeds, you get another variety, which could be very similar to the parent but it's not the parent. The gene pool is different.
Shin-Deshojo is a Japanese maple variety similar to Deshojo, hence the similar name. Shin-Deshojo is supposed to be more resistant to diseases.
A seedling is a young plant grown from seed.

Yes, I know thats how it usually is and how we want it to be, unfortunately DNA tests might disappoint you. Actually Shin Deshojo is one example where Ive heard iseli nursery is selling seedlings or a seedling from what might have been the original Shin deshojo clone AS Shin deshojo. Should not be done of course, but in that case Deshojo seedlings also seem possible
Aside from that, in my opinion its bad practice to pick a cultivar name that contains the name of a previous well known cultivar if its not directly related. Especially if your pitch is "its the old thing, but improved".
Hence my assumption
Looking up Shin Deshojo in the Vertrees/ Gregory book, the wording is "Shin means new, indicating that this cultivar is a later, improved selection of the well-known Deshojo."
Could be interpreted in 2 ways. Either Deshojo is understood as a clone and selection of Deshojo means seedling, or Deshojo is understood as a phenotype like Arakawa apparently often is in Japan, and Shin Deshojo just means great new specimen clone of its type (Deshojos, which would be used how we use Corallinums, perhaps a subgroup of that)
Have you seen a tree-sized Deshojo? Peter-chan has one, I dont remember if hes shown it with seeds.
P.S.: More from the book (deshojo entry): The shojo part of this cultivars name [...] can become confusing. 'Shojo' is an old standard form of the red palmatum.
Deshojo as described here, is the base for other selected cultivars. Shin deshojo is a newer selection.
So that leads me to think its indeed a seedling from Deshojo, and Deshojo is fertile.