Does each Pokestop offer only 1 type of evolution item?

I work at a Beach Resort. Everyday I leave the hotel at 12 midnight and head to the only Pokestop on property. This one in particular has only offered “Upgrade” (The evolution item depicted as a yellow computer chip). I now have 8 of these.

I am starting to think each Pokestop has one particular evolution item. Is this a common phenomenon?