Hello Peter,
Hopefully you are the same Peter N I've met in Budapest long time ago.

In my opinion for the unlisted components you should determine the SIF and apply them.

For the listed components the code (at least 2018 ed.) specify as being 1. in absence of more applicable data.
Now, the point is if the manufacturer can not be pushed to provide these SIF as being a special component. I would go this path.

Best regards,