It's really trial and error!
I was diagnosed with fibromyalgia before I started hrt. I also have rheumatoid arthritis. I definitely have RA (my poor old twisty fingers!) but the fibromyalgia diagnosis doesn't seem so relevant as I can now actually function with HRT whereas without it I was mostly immobile. My RA is also improved with the HRT but obviously not reversed.
Often other issues are exacerbated by peri menopause. Hormones are funny things, they basically can affect wide areas of your body and mind. (Sorry for my most unscientific information there). There is a severe lack of information about menopause other than basic symptoms lists, women are literally relying on each other's experiences to make the decision about HRT.
My point being that even if you do have another diagnosis, HRT can still benefit those symptoms, therefore you can attribute the worsening of other issues to peri menopause