Even if they were part exchanged, the fact that First of all companies are taking second hand 05/55-plates in 2019 just shows how desperate they must be.
Surely they would have been able to find something through the usual group cascade if they were in need of additional buses?
Saying that, they did have similar E300s before (SN03 WMJ / WMU) , except that they were owned by Falkirk Council (along with three Mini Pointer Darts which would occasionally change operator if certain contracts were given, the E300s always remained with First) and all ended up being sold years ago as First weren't interested in buying them outright when the Council didn't want to own them any more.