I would agree with the trapping issue, I don’t know however that its something you can adjust for in prepress and here’s why: We print books in volumes by years with color tabs on the spines that denote each year, those tab colors were picked from a Pantone swatchbook and cmyk seps made by converting in Photoshop and getting the values, years ago, some colors match close while others are a little off, 2 or 3 that we print that have high C and M percentages with very little K give us big color shifts on press at times. The densities can be perfect on the scanner but the color changes from purple to blue to everything in between and our press operator never sees it and it doesn’t get caught until coming off the collator, but that’s a different story, just passing on what we’ve experienced with those colors.
We print G7 and use a maxGCR. Those same colors, only darker, with some K to them, don’t have those color shifts.
Just went thru some testing last week and made up new seps for those problem colors by converting it to how we run now with the high GCR and those colors now have some black in them and didn’t exhibit the problems. One of them was even 78 points less ink separated that way. It was our “1959” color which was originally chosen as PMS#448 and sepped as C-87, M-72, Y-100, K-0, when reseparated using G7 profile and maxGCR it came out as C-39, M-16, Y-57, K-69, so you can see our CM trapping became a non-issue. Not saying this works for all colors but you may try it and see what happens.
Some colors as you know will not be a perfect match no matter what you do. I’d say most will not be and some will be worse than others and some won’t be close enough to use, so those are unmatchable colors, unless you customize the cmyk combo to get closer. My experience is I couldn’t do better than all this expensive software can do.
Just our 2 cents