Detectability of the predicted disc-sculpting planets (Sect. 3). Horizontal axes show the minimum planet masses required to sculpt the discs if debris clearing is performed by one planet (left plot) or by multiple, equal-mass planets (right plot). The vertical axis shows sculpting planet masses divided by our L′-band detection limits at the apocentres of those planets (assuming the best-case scenario, where the systems are face-on to the observer). The dashed lines show unity. Symbols have the same meanings as in previous figures. If the discs are each sculpted by one planet (left plot), then some of these planets will lie at or close to the current detection limits, and a factor of 10 improvement in mass detection limits could yield many more predicted planets. Conversely, if instead each disc is sculpted by multiple planets (right plot), then these planets could be significantly smaller and many might not be observable even with significant improvements in detection limits.