Over the years, I’ve come across a fair number of inexperienced academic authors with a less-than-sound grasp of their responsibilities regarding the re-use of their own work in other publications. I have to remind them that the moment they sign a copyright transfer agreement the work is no longer theirs to use as they see fit.
In all fairness, not everything about text recycling is as black and white as this, so it’s good to know that the Text Recycling Research Project (TRRP) exists as an authoritative source of advice on what is and is not an ethical approach to re-using one’s own work in other projects. Check out the post by Cary Moskovitz and Michael Pemberton in EON, to find out how the TRRP undertook its research and what resources it can offer: https://eon.pubpub.org/pub/vqpv47ui/release/1.