The 20p with coating - 1943 - has a not so obvious coating, at least when used, and the watermark is an orthogonal one with a symmetrical paper wire! Best compared with the 1943 July Revolution stamps!
The density is 30/16 - the 16 horizontal lines per cm should result in about 16x3.75 = 60! A quick rough count for this stamp comes to 61! All the other paper wires - except for the "Tela" - would give 20x3.75 = 75! Which is a lot more!