Abundance of SNR, KNR and EKNRs. Top: Number of systems observed by an all-sky radio survey per logarithmic unit of age, $\frac{\mathrm{d}{N}_{\mathrm{obs}}}{\mathrm{dlog}t}$, for SNR, KNR, and EKNRs. Bottom: $\frac{\mathrm{d}{N}_{\mathrm{obs}}}{\mathrm{dlog}L}$ for the same cases as in the upper panel. For the SN case, we show $\frac{\mathrm{d}{N}_{\mathrm{obs}}}{\mathrm{dlog}L}$ for the coasting regime in grey in order to highlight its non-monotonic nature. We assume a minimum flux threshold of F_ths = 1 mJy, an observation frequency of 3 GHz, and fiducial ejecta parameters as in Fig. 1. EKNRs evolve on a short-enough timescale for their evolution to be observable (as explored in more detail in Fig. 5).