They are independent of each other but they were developed on the same machine in the same database but with different tables.
Whilst delevoping I had 2 working modx installations with different prefixes and once it went live it went back to 2 databases but maintaining the unique prefix.
The file structure hasn’t changed. A subdomain on the host is just a subfolder from the webroot.
I’ve hopefully left it open for a consolidation at some time in the future and with some jiggery pokery I may be able to meld the tables together

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