Sag, you can definitely have AS before it shows up on radiology, but many doctors won't give a final diagnosis until they see signs of it on film (x-ray or MRI). I can testify that you can have very bad inflammation and pain and little sign of it on the films. Pay attention to your CRP blood test. That usually tells you and your doctor more about the current state of inflammation. The way I see it, once the inflammatory process starts you have the disease. It shows up on x-rays only after physical damage to your joints has been done. This can happen in a few months or it can take more than 10 years. Everybody is different. Some just get shadows and lesions, others get obvious fusion of bones. But generally it takes years to show up. If you are a woman you are much more likely to get misdiagnosed or given a tentative diagnosis because of bias that AS is mainly a man's disease (and more so if you are B27 negative). As long as you can get the proper medicines, having or not having the diagnosis does not mean a lot at the end of the day. In fact, if you do not have a diagnosis, but you get better after taking NSAIDs, then that is one more evidence that you have a rheumatic disease. Some doctors hold off on the DX until they see how you respond to therapy for a few months.
DXed with AS 30 years ago