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I know there's a post floating around here with a rough conversion chart for paint brands.
I've found one that's better, and covers most of the major brands.

https://www.patreon.com/posts/21020021

It might have more paints featured, but , from an admittedly cursory look at the Reaper sheet, it's accuracy is way off.

It states that it's based on colour swatches provided by the companies (presumably that means digital), which would explain a lot.

Reaper Deep Ocean isn't remotely comparable to Vallejo Heavy Charcoal or GW Dark Reaper. Ditto Reaper Red Brick and GW Screamer Pink or Coat D'arms Amethyst Pruple.

Yes there are some accuracy problems. Most notable are in the VGC Heavy paints, which according to Vallejo are just rebranded VMC paints. Only one I believe shows an exact match between the VGC and VMC paints and two of them have different equivalents than what Vallejo says are the equivalents.

If you take a look at the 'Delta E00' number, the closer that reaches zero, the closer the match will be.

This has worked well enough for me, and it's certainly better than what's currently being shared.
If it's not helpful to you, oh well.

For GW’s Base paint range, you won’t find anyone close than INSTAR.

On topic though, i’m surprised that companies gave you swatches as that’s something we would never consider doing. Regardless though, some of the colours are a little off and as stated above, looking at the dV value is always going to give you a better indication of how close the colour s than a digital swatch, mostly because monitors and screens vary so much that a digital swatch will never look how it’s supposed to