The prospect of there being traincrew who don't sign 197s is very far-fetched to me.From RTT 1W63 appears to have been mk.4s, which then worked 1V66 as far as Crewe vice DMU - according to RTT 197015 off a 1Z22 FROM Cardiff vice 1M22 detached at Picc ran ECS to Crewe to replace the hauled set - surely they don't haven conductors not right 197s?
Perhaps heavy loadings were expected on 1V66 as far as Crewe, so it was thought better to use the mkIVs for the busy section and then replace them with a 2-car 197 for the quieter section of the run to Cardiff?
The workings for 1V66 always seem to be a little iffy, and this is generally due to the service being formed of a portion of 1W22 which is obviously not possible if 1W22 is short-formed (which often occurs during the day) and the mk IV ECS off 1W63 being timed close to 1V66 as far as Crewe.