No problem, keep asking!
Yeah there are different theories on this issue.
I think/believe that essentially, Enneagram types (tritype, stacking, core etc.) do NOT change.
However, as you said, health levels can and do change, which can make people express their type(s) quite differently.
Also, it seems like we can use our instincts and tritype fixes to some extent dynamically or flexibly, depending on what a specific situation requires, what kind of life obstacles you are facing rn, etc.
For example, if you are in a situation where food is scarce, or you want to lose weight, you'll have to rely on your SP instinct; and you'll occupy your mind with SP matters, even if you are SP blindspot.
Or if you are faced with a confrontational situation and you are a 9 fix, you will likely act like a 9 core in that situation, but otherwise revert back to your main type or second fix, depending on what is going on...
The origins of the Enneagram are rather mysterious and vague, and I cannot tell you why it is 9 types. ^^'