Is there an official specification for the point cloud data (PCD) format? Or is it rather only intended for PCL-internal use? The only information I found about it is this which kind of looks like a specification, but it doesn't contain all the information needed.
I might want to write a PCD loader library (independent of PCL), but maybe this is discouraged?
Naturally, PCD files are mostly used in PCL-enabled applications written in C++. However, there are loaders implemented in other languages, for example Python and JavaScript, so it is definitely not just a PCL-internal format.
To my knowledge, there is no official specification besides the one you already linked. And indeed, it is incomplete, for instance the binary_compressed data storage format is not mentioned at all. I would suggest to use the PCL implementation (which is fairly stable) as a reference and resolve any ambiguities in the linked document by checking how the code works.