As far as my tests go: Recycling products are always placed into the recycler's output slots in a specific order. Recycling Low-Density Structure (LDS) will always produce steel in the first slot, copper plate in the second slot and plastic in the third slot.
If you empty out a recycler and recycle ...

I support this proposal.
My use case is that, in a book full of parameterized blueprints where you select the result of a recipe (e.g. to turn iron plates into gears, you click on the gear recipe), I want to add a blueprint that uses a furnace to turn e.g. iron plates into steel, but the "iron plate ...