'Shindeshojo' is certainly a possibility. There are thousands of named JM cultivars and thousands of more seedlings with no registered name but differences from the classic ''average JM''. Not having a label, breaks the provenance of the tree. This is no more valuable than a pedigree dog that lost its papers. No matter what, a paperless pedigree dog is worth no more than the mutt at the animal shelter.
You can guess, but you need 4 seasons of photos for comparison. Spring leaves, and your observations on length of points, number of points and colors is excellent. Summer foliage especially the degree of fading of the spring colors. Autumn color. Winter color of young twigs, bark of older trunks and branches, and the color of the flowers in spring, and whether flowers hang below their branch or curve up above the branch they come off of. Once you have this list of traits. Compare it to the list of cultivars the source nursery is known to have had over the age of the tree, and consult a book like Vertree's, to get the fine details on what traits each cultivar has. You can narrow down the likely hood. But without a provenance, you really can not say with certainly what the cultivar name is.
And the last complication. Seedlings from named cultivars, can not be labelled as that cultivar, because a seedling is always a genetic re-assortment of both the pollen and the seed parent. In the case of a self fertilized seedling, it is still a reassortment of its seed parent's genetics. It may resemble its parent in a number of features, but will always differ in one trait or another. In which case it can only be named Acer palmatum. Period, no qualifiers. Unless one were to register the seedling as a named cultivar. Which is only worth while if one were going to propagate and sell the tree.
SO, yes it might be 'Shindeshojo' it might be a random seedling. Hard to say.
Provenance, or name, does not change the beauty of this tree. It is a wonderful looking maple. It should become a beautiful bonsai.