SWO: The terminology of cerebral ischemia is currently under discussion and partly changing, nevertheless, I do get the idea from looking into more recent statements, that this isn't final yet. But you are right, the PRIND isn't that much used recently, nevertheless if you search for that in medline, you will still get current citations.
At the end, it is somehow semantic. The underlying pathophysiology of whatever you call it, is a lack of oxygen supply, most commonly by occlusion of a vessel of varying diameter, or, less common, by hemorrhage. The latter is not the case for you as well as for Rick, because MR would look differently.
The current discussion for always calling it a stroke, I have the feeling, basically results from an identical pharmaceutical treatment for both, except if any type of reopening procedure would be used, what one would only do in a stroke. In a TIA, the affected area must be small enough to allow neurologic remodeling, while in the full blown stroke the area affected in general is larger, not allowing a fast and full recovery to normal. For both there is an increased risk of a second or full scale stroke, thus pharmacotherapy is aimed at preventing this.
Now, if your goal is to improve the outcome, which best is achieved by treating all patients, independently of the severity of their clinical findings with protective pharmacotherapy, than it seems logical to call all clincal findings a stroke. In former times, when CT and MRI wasn't that widely available, you wouldn't be able to see the underlying destruction, thus the differentiation of the stages was done on a clinical basis. In my personal view, treatment is wider than just pharmacotherapy, and patients with a stroke generally would also need physical help in regaining as much brainfunction as possible. That is not needed in TIA.
The term TIA is most certainly not (yet) obsolete, and many doctors will interpret a diagnosis 'TIA' differently than 'stroke', thus it is in my view a legitimate offer in the hope to regain your medicals. It doesn't guarantee, but it surely doesn't hamper the process.
To your further questions: usually you wouldn't need a second scan, just a second reading will most of the time suffice. Interpretation of typical findings in brain MRI is not that difficult, nevertheless, in the individual case it might be chalenging.
If you have no risk factors, one thing you could look for would be Lp(a), a special lipoprotein which seems to be involved in quite some patients with atherosclerotic disease and no other risk factors.
Are you a diver?