If I fill out a sheet for a product with a particular recipe then make a new sheet for that same product, the two sheets will synchronize changes. I'm not sure if this is intentional but it makes it impossible to compare options.

Initially stumbled upon this while playing Nullius, but you can replicate this in Vanilla by creating two sheets for 1/s plastic and selecting two different petroleum recipes. Upon compute, the recipe selections will switch to one of the two.

I thought it might be related to the product slots so I put 1/s wood in the first slot of one of the sheets, bumping the plastic down to slot 2, but they still synchronize.

Unfortunately, it's a limitation of the mod's current design. Each product is associated with one unique recipe at all times. Changing that recipe triggers a general recalculation, so it's updated everywhere.

A potential quick fix would be adding a "Freeze" button on the sheet that freezes its contents in place, preventing it from changing on recalculation (such as when updating a recipe in another sheet). When unfrozen, it is recalculated as normal.

Another option is to have a different recipe and machine mapping for every sheet. When creating a new sheet, the current sheet's mapping could be copied over and evolve independently from there.

Which option do you think would be better?

The latter option is better since, intuitively, users will assume two sheets are not synchronized unless some indication is given.

If the former option is less work for you, adding some indication that recipes synchronize by default would be helpful.