In a previously-published paper we have one chart with about 6 traces — a pair of controls, and four test subjects. We are now preparing a follow-up paper in which one of the test subjects now acts as a control, with another half-dozen new traces compared to it. Assume that each of the experiments is technically valid (i.e. presenting either figure alone would be fine in terms of replicates, stats, setup, etc.) Is it OK to re-use the data for the shared trace in both papers? We would prefer not to repeat the whole experiment — aside from cost, there's an ethical issue (animals are involved and we want to minimize suffering). We are tentatively thinking that we can re-use the data along with an explanatory note ("Trace X in Figure 3 is re-used from reference Y") but I'd appreciate other thoughts.
Looking for guidance in journal instructions, I find that at least one journal-running society says
In the event that the authors' previously published figures and/or data are included in a submitted manuscript, it is incumbent upon the corresponding author to (i) identify the duplicated material and acknowledge the source on the submission form, (ii) obtain permission from the original publisher (i.e., copyright owner), (iii) acknowledge the duplication in the figure legend, and (iv) cite the original article.
That makes it clear that some data re-use is acceptable so long as it's clearly indicated as such. The journal also says
It is incumbent upon the author to acknowledge any prior publication, including his/her own articles, of the data contained in a manuscript submitted to an ASM journal. A copy of the relevant work should be submitted with the paper as supplemental material not for publication. Whether the material constitutes the substance of a paper and therefore renders the manuscript unacceptable for publication is an editorial decision.
which makes it clear that it's not a blanket okay, and the editor will use their judgement as to how much is acceptable.