Anyone sampling grain on set or using external grain to comp?

Hi,
recently i’m receiving from colorist footage with added grain from color sw plugin.
Usually we do comp before grade but sometimes is the other way around.

Let’s say i could have for some shot a grain version and a clean version (just original footage grain).
I was wondering if there is an “good practice” for getting some sort of grain sample from the colorist and apply it to the “clean version” and get the same result.
I was thinking about some grain on black or gray scale chart in order to use it on the elements to comp.
If that makes any sense, could be useful to make also some sort of grain plate, or scan grain on set for each shot? Anyone have experience on how it should be done?
oooooor…
Doesn’t make any sense to use an external scan grain since it doesn’t give any indications on how it should show on hi-mid-low part of the image?

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Ask the color house to give you a un-grained and grained pass over a frame of grey or black. If they can do that, a subtract between the two will return the grain that you can then add/screen to your comp.

That said, I don’t like it when the grading folks add grain. I get that they want to please the client and a grain pass can help with getting an approval but it ultimately makes more problems in composite and finish (here, comp always happens AFTER the grade).

Thanks Chris for your input. I asked the color house to supply a “clean” version with no grain added for the shot that i know i would be need to work on. I’ll try the gray-black frame to see if i can get any closer to what he apply. I’m afraid he played around with grain a little bit and apply it mostly on brighter part of the image.
I guess it wont be a straight forward operation. I’ll get back with the result.
Thanks