I've seen it only in very few instances that the dwell volume of the original system used has been stated in an EP monograph. That said, it's of course very hard to adjust the gradient to an unknown dwell volume difference

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Fortunately (and wisely) absolute retention times are very seldom part of the system suitability test so, in my opinion, as long as you pass the system suitability and the separation works, no adjustment is necessary. I'd start to care about gradient adjustment only if problems actually arise. Then, if you don't know the original dwell volume, retention times stated in the monograph or an example chromatogram from the knowledge database (if available) may give you a clue in which direction you have to adjust the gradient. The rest is trial and error, ahem, I meant empirically-based development.