Why 2 vosa vans

Came off jct 31 m6 down to r/o and vosa van pulls up alongside with follow me sign on it for Lorry behind ( normal stuff ) but behind Lorry was another vosa van ( beacons going etc ) , vosa bloke in van in front jumps out and I assume goes back and speaks to Lorry driver and that’s as much as I saw of it .
I’ve been pulled a few times but just by the 1 van in front with follow me , not seen one in front behind , is there a reason or just me not having seen 2 vans , ta