Soapcalc fatty acid numbers are only for a selected range of fatty acids (FAs). They only show you the most common FAs found in typical soap making fats. So if the combined % of FAs reported by Soapcalc totals less than 100%, you can't assume the missing % is due to unsaponifiable chemicals.
One example: Coconut oil contains roughly 15% of two short-chain capric and caprylic fatty acids. These FAs contribute to the harshness of a coconut oil soap. Soapcalc doesn't report this FA content.
Another example: Milkfat (butterfat) contains a small % of very stinky butyric acid, but it only takes a small % of butyric acid to make an unpleasant smelling soap. This FA, another short-chain FA, isn't reported by Soapcalc either, so it's tempting to make a recipe with a large % of butter only to end up with soap that doesn't smell all that good.
And on the other end of the FA spectrum: Canola and rapeseed oils contain erucic and benhenic acids, two long-chain FAs. My notes say canola can have up as much as 9% of these FAs. Some varieties of rapeseed oil can contain quite a bit more, especially erucic acid. Again, Soapcalc doesn't report information about these FAs, which can skew people's perceptions about the properties of soap with a high % of canola or rapeseed oil.
One of the discussion threads listed above has a comment that fat with a higher unsaponifiable content will have a lower saponification value.
While that's true, it's not the whole story. It's also true that other things contribute to the lower sap value. In particular, the sap values drop as the fatty acid molecules get bigger. The liquid oils with high % of oleic, linoleic, and linolenic FAs have lower sap values than the solid fats with more-saturated FAs -- fats rich in palmitic, myristic, palmitic, and stearic acids.
For the most common fats used in soap making, shea butter and avocado have the highest % of unsaponifiable content. My notes say shea around 4-9% and avo at 2-7%. Both will have higher unsap content if unrefined and lower unsap for refined. Most other common soap making fats have low % of unsaponifiables -- in the range of 1-2%.
I think it's unrealistic to assume ALL the unsap content in a fat will be beneficial to the skin. It's likely that some is, but it's also likely that some is not. While I'm no expert on this topic, I do know unsaponifiable chemicals can vary widely. To really know whether the unsap content is good for the skin, you need to know the specific chemicals and know what they do for skin.
