The pleasure is all mine!

Thanks, the poses-modified, one of them used outside their intended expression-came from

https://www.daz3d.com/z-utility-laughing-and-crying-poses-and-expressions-for-genesis-3-and-8
https://www.daz3d.com/talking-to-you-poses-and-expressions-for-genesis-81

I very rarely make a pose completely from scratch, but usually modify and repurpose poses from packs. I'm wondering what the etiquette on crediting that is, especially when I suspect I'm traveling well outside their original intents?

Well, if I use a pose as starting point, I write, where the origin comes from, but that I've modified the pose.
Most of the time one has to modify any pose, cause they just don't work all the time. Some vendors are better than others, one of my favorites is Zeddicuss (your first link to).
And what the intent of a vendor was isn't important, as long as you can use the pose and work with it. Important are satisfied customers, they use to come back

That seems fair. Start with ship of Theseus, end and credit with "modified ship of Theseus".

Zeddicuss is the G.O.A.T. They really don't shy away from say, cleaning or other more 'everyday' scenarios.

Useful poses, and not these weird poses, a woman would maybe use in her private walls under special circumstances and even then *lol*
When I scroll at Renderosity, I really wonder, where they even get the ideas from to create poses, impossible to use if one wanna make an "everyday scene render".

LOL. It takes all kinds to make the world go around, they say

Oh, and I thought money makes the world go around