Radio spectra of the cores of the 26 sources in the sample. Flux density measurements from LOFAR image at 150 MHz (LOFAR-IB in purple and LOFAR6 in blue), FIRST images at 1.4 GHz (in red), VLASS images at 3 GHz (in yellow), and VLA at 3 GHz and 6 GHz (in orange and black, respectively; only for two sources; see Appendix C). Triangles indicate upper limits. Restarted candidates are indicated with a green title, and the rest belong to the active comparison sample.