I feel like an idiot because you're absolutely correct, and I've even used this recently in Bambu Studio (which I believe is forked from PrusaSlicer, so it may be there as well). I haven't used Prusa or Orca slicers, but it is somewhat limited in Studio, especially when printing "per object" instead of "per layer"
I'd still recommend OP print one benchy at a time because it's very easy for one object to wipe out the entire print bed of parts if misconfigured.
They have all the parts available on their site.