I thought this was the case as well, but now I'm not sure.
A friend of mine had taken the OAT in mid-September and planned to retake it as soon as she could. I took mine for the first time in late January and told her to take it with me. It is well after her 90-day waiting period, but she decided that was still too soon, and so she declined.
After I took my exam, I was very satisfied with my score. So I felt it was okay if she discussed her exam with me since I didn't plan to retake it ever again. It turns out we had the exact same test questions and reading passages as far as I could tell. Even allowing for a huge test bank, that is still a big coincidence.
Of course I joked about how she should have taken it with me then. But surely they wouldn't have given her the same exam? Maybe they also have a system in place to make sure you are given a different exam than the previous, and the 90-day thing is for some other reason.