The hardtack recipes added/modified by Baketorio+ have extra byproducts in the form of bags or wooden chests, however every vanilla furnace only has 1 output slot, so it's impossible to actually get the byproducts out. Beyond that, it also tricks Factoriopedia and Factory Planner into thinking that there are no machines that can craft the recipe, making it harder to plan things out.

Shoot, sorry, will fix that ASAP as soon as I’m home! I’m so sorry

Apologies for the delay; I wanted to test that it worked and build a little wool -> bag set up for testing, and also fixed some names and icons.
The update it up though with the furnace fix.

I noticed that it actually should only need 2 output slots, but only if the two identical outputs were merged into a single output with an extra_count_fraction field. That change was also what prompted me to go through and add ignored_by_stats and ignored_by_productivity to every recipe catalyst, at least for obvious ones. I haven't done any for two step catalysts (yet).

Well, the only one that needs 3 is the flour bags to hardtack because to keep the 80% return for the bags, instead of just having the same quantity at 80% probability (like a sane person), I did it at 1 guaranteed and 1 at 60%; all of the recipes with bagged ingredients follow that same method as well.
So, that's 3 outputs total. And it should be good for any additional mods that add furnaces (as long they load first... might need to put that part in the later loading actually...) as it just goes through all furnace objects and sets the output slots to 3 if there are less than 3.

extra_count_fraction does exactly what you want. It gives the listed amount 100% of the time, and then gives a chance to give 1 extra, with the chance being the value of the field in question. The way you currently have it implemented was needed in 1.1 since this field didn't exist back then, but it was added in 2.0, likely for the recycler, which is supposed to handle cases where it's supposed to give back 1.25 or 3.75 of an item if 5 or 15 of said item respectively were used in the recipe for what's getting recycled.

My local patch put the output expansion code in the otherwise empty data-updates.lua, though an argument could also be had for data-final-fixes.lua.

Sorry for the delay. Thanks so much for that, I didn't realize that stat was there!
I've since updated the bag returns in the recipes to use that stat, only requiring 2 furnace slots minimum, and updated that part accordingly too.
Also, I indeed moved the furnace mod to data-updates; I had considered that before but just didn't do it, but it's safer/robuster that way XD