The code that creates CP/M-86 (not multi-user) and CCP/M-86 (multi-user) are very similar. Some versions are publicly available. It is possible to download and compare.
All Multiuser capabilities of CP/M, MP/M, CCP/M were for a 4-Bit User (0x0 to 0xF), expressed directly in the stored filesystem FCB format, set by the TPM and inherited by processes. Some fallback file search support existed to User 0 for System Files. No "group" identity ever existed for CP/M. Please double check the CCP/M OS documentation which is available. I re-read to (re)confirm my memory.
(before my involvement...)
CCP/M-86 3.1 existed. Supported only CP/M style media.
CCP/M-86 4.1x existed. Supported only CP/M style media. Internal hints of CDOS :-).
CCP/M-86 5.x existed. Supported CP/M and DOS media. Re/Co-branded Concurrent-DOS 5.x.
CDOS 6.x existed. Supported DOS media. CP/M media only via CPM.CMD.
At the time there were OTHER 286 architectures than the PC that DRI Supported. There was an interesting one, by Jarogate (Liam antennae alert!) - the Sprite. It was many times faster than other platforms, so it was being used by DRI for some primary development work. It was a modified S-100 based system and supported a full 16MiB of memory. But CDOS could not use it...
As a Jarogate intern I spent a few weeks during a 198x summer with a rented HP logic analyzer working out what LOADALL (and other opcodes) did. This was based on some photocopy-fax-phlotocrapy-pfrax almost illegible document titled "MIPO News" which had teaser info, but not much more. At the end of my research I provided an ASM file of what LOADALL did and how to use it... I'm pretty sure it was given to DRI.
CDOS 6.x XM. existed. Supported DOS media. LIMS memory + [LOADALL HACK]
If you had a Jarogate Sprite running CDOS 6.2 XM, then it supported a full 16MiB of memory. I still have my Sprite, but it is not currently running :-( due to controller / disk problems.
The Jarogate sprite used an AMD 12Mhz CPU. I do not know how this maps to the Intel versions. But, I think this is where some of the compatibility problems for DR started!
The virtual console system of CCP/M was revolutionary and amazing. It does not get enough credit.
There are perhaps other untold stories of how DRI was trying to move away from hand crafted ASM and PL/M to other high level languages.