This is complicated to answer. Power Spots come from two sources: imported data that can only be used for Power Spots, and accepted Wayspots that are not eligible to appear in Pokemon Go as Pokestops/gyms. (See here for an explanation of that: Clarifications on Pokémon Go Power Spots ) The import seems to have been a one-time event.
You can check to see points of interest that already exist by beginning a nomination while you are physically right at the location. In the “Set location” map screen, with the toggle in the bottom left corner on, you can see all the Wayspots there. Ones not used as a Pokestop/gym will show as exclamation points (!), with the statement “Wayspot used in other Niantic games” when you tap on it. (I don’t like that wording, but that is what it says.) This feature does not work remotely, and the coverage area is small, so you must physically be right where you want to check.
A Wayspot that has been through the Wayfarer review process, and would be a duplicate if nominated, will look something like this.
The imports were only ever eligible to be Power Spots, even if alone in an L17 S2 cell. (See Why an accepted Wayspot may not be used in Pokemon Go (S2 cells and Pokemon Go) for more about that.) Community reviewers will not see these imports when they are reviewing nominations. These imports originally had a placeholder picture and no description when they were added to the database, like this.
Since trainers can edit Power Spots, a photo and a description could be added to the imports, so you can’t always go by the lack of photo and description. But if they have that placeholder picture and no description still, you know it was never eligible to be used as anything except a Power Spot. I actually found this exercise business in this example and submitted it because of the Power Spot import. I can confirm that it was not rejected as a duplicate.
There are other cases where imports were made to provide Pokestops/gyms, which I can’t speak to, since this did not happen in my area, and I am not familiar with them. But that will make this issue even more complicated if you are in an area that has those.
Edited November 19 to note that the new Webform Submit option is not displaying the Imported Wayspots on its nearby check. If you use that option, you don’t have to worry which is which.
