Things you miss and things you don't

[Knaight]

Okay, that explains why 10 siders aren't really polyhedrals now what about 20 siders that go from 0-9?

Equilateral triangles, 0-9 is printed twice. The d20, d4, and d8 all use equilateral triangles in different conformations. The d6 and d12 use squares and regular pentagons, respectively.

Also, the term "true polyhedron" should probably be read more as platonic solid. The Wikipedia pages for that and similar topics are actually pretty solid, and unlike most math on there they're written in a way that's comprehensible if you aren't already familiar with them.