Longshot has released version 1.6 of the Amstrad CPC CRTC Compendium (July 2023) which is a documentation about the CRTC 6845 (and some others circuits). Note that the CRTC is a generic component used in several computers including the IBM PC.
It is possible to check if an emulator is good with the SHAKER tests by Longshot. SHAKER is a program designed to run on CPC machines produced by AMSTRAD in the 80s-90s. The objective of this program is to carry out extensive tests on the video circuits of this machine. These video circuits are the GATE ARRAY and the CRTC 6845. AMSTRAD produced several series of GATE ARRAY and used CRTC models produced by different manufacturers (HITACHI, MOTOROLA, UMC, AMSTRAD). This has been causing compatibility problems on operations that exceed the functional specifications of these circuits. The identified CRTCs are numbered from 0 to 4.