Which 'JAR-FCL seminars' might those be then? Or do you mean the FI seminars? Which are run by service providers, not the CAA.
My view is that it is an extremely good idea to conduct navigation refresher training or IF refresher training during the 'dual training flight' - that, after all, is the whole idea of that flight - training!
Whereas the re-validation LPC or renewal LST for the SEP Class Rating should only be conducted in accordance with Schedule outlined in SRG\1157.