I would liketo publish old data and original results never published from my Ph. D. They continue to be relevant since the field of research on pristine DNA damage by ionizing radiation moves slowly.
I think you can proceed in the normal way here. Just describe how the data were obtained (and processed, if applicable). If everything was done a while ago and you're writing it up now, but not doing any more experiments/analyses with the samples, then everything should be okay.
If, however, additional work has been done more recently, so that a time lapse between different stages of the data processing and/or experiments may have had an impact, in one way or the other, on the results, then that should be mentioned and discussed of course. For example, if there is a suspicion that the damaged samples may have deteriorated even more in time, then that should be taken into account.