As I understand it someone did research and did scans or ultrasounds of some arteries of patients with PMR and found changes that looked like GCA but the patients did not have symptoms. I do have one of the symptoms, a headache at my temple that wraps partway around my eye, but a negative temporal artery biopsy. Who knows what is going on with this disease!

Generally speaking it is patients without outward signs and symptoms suggestive of GCA. However, when other means of detecting GCA are used like temporal artery biopsy and/or ultrasound, GCA is discovered.
https://pubmed.ncbi.nlm.nih.gov/37129541/
It basically means people can have GCA and it isn't detectable. Even temporal artery biopsy and ultrasound aren't 100% reliable for diagnosing GCA.

I have never been officially diagnosed GCA but there was some evidence that I might have it somewhere. Large vessel vasculitis (LVV) isn't confined to the temporal arteries so that opens up other areas to look for vasculitis. It was one of the reasons why I was approved for Actemra. The recommendation was to "assume vasculitis" and treat me "as if" I had GCA.
https://pmc.ncbi.nlm.nih.gov/articles/PMC9115766/
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I actually had all the signs of symptoms of GCA but they could be explained by other conditions. Uveitis for the visual disturbances and trigeminal neuralgia for the facial pain. Both of these condition had an inflammatory component and were exacerbated when my inflammation levels were too high. Both of these conditions responded well to prednisone. These two conditions responded better to prednisone than PMR did!