tanach - Why does the Tetragrammaton sometimes include the cholam vowel?

Why does the Tetragrammaton sometimes include the cholam vowel ?

The question isn't a duplicate of What are the reasons or rules for the different variations in vowels on the Tetragrammaton?

Because that question was very general. This question is far more specific.

I understand (from the answer to the previous question), that and when, YHVH is written with vowels like Adonai, and when it is written with vowels like Elohim.

What I would like to know is why is it sometimes written with the cholam, and sometimes without?

Is there any kind of rule that governs when it is written with a cholam and when not, rather like there is a rule for when it is written with vowels like adonai vs vowels like elohim?

Funnily enough, I just noticed that while my copy of the text which is the WLC(Westminster leningrad codex), which now is essentially meant to be a copy of the leningrad codex, has mostly without (like thousands without), and some with (like between 50-80 with). Mechon Mamre don't have a cholam on any of their YHVH instances. Whereas bible.ort seems to have the cholam on every single YHVH instance!