While mods generally don't change productivity for other recipes, if they do, it can cause free items.
I bring this up specifically because my mod "janky-quality" disables quality for catalyst parts of recipes, and in our case we do not, allowing for free quality bonuses.

Sorry but i don't actually know what you mean by catalysts. What implications does it have to the mod if it's set and how would one go about changing it?

My mod's all compressed items have "compressed-" at the beginning of their internal name if you have a blacklist. Recipes begin with "decompress-", "compress-" or "smelt-compressed-".

They are also added to module.limitation list by:

function SimpleCompress_AddProductivity(_recipe)
for i, module in pairs(data.raw.module) do
if module.effect.productivity and module.limitation then
table.insert(module.limitation, _recipe)
end
end
end

Because i knew these recipes should not allow productivity modules in the assembler.

I just give few options, you may have many other mods to hunt if you don't make Janky-Quality "mod proof" :) In any case it is just a temporary mod before the official expansion.

Thanks for the answer!

Someone asked about compatibility of my mod with yours, and I wondered why it didn't work as expected, so I investigated and saw that.

In general, when an output it marked as catalyst i.e. result property "catalyst_amount" exists and greater than 0, that part of the recipe automatically gets ignored by productivity bonuses. This is how it works with Kovarex Enrichment Process, where only the 41th 235 gets productivity, while the first 40 don't.
In my mod, I made it similarly, so only the e.g. 41th 235 can get quality bonuses. Similarly, barrel recipes don't get free quality when barreled and unbarreled.

My recommendation is to add "catalyst_amount" to the outputs for compressing and uncompressing, which will work for my mod
It can also help with mods that add productivity to recipes that usually don't have them.
It's a niche case, but it's probably a good practice to mark item conversions such as these as catalysts.

Thanks again.

Finally had some time and i think it is working in my test now. Uploading soon™.
https://i.imgur.com/zzRlkAc.png
With previous version of the mod the same recipe created multiple qualities of the compressed items.