Hello Stéphane,
I have compared the registry settings you've mentioned for the PC with and without bitlocker encrypted drives and, unfortunately, found no difference, meaning that the registry settings are identical :(
I have googled, and it looks like that is not possible to pull the value from the registry which indicates the status of the HDD encryption
Just in case you have other ideas, please let me know
Thank you very much,
Rostyslav