Yes it’s happened before. Right time, right place for those that scored it in the first half of this calendar year. Not sure it’s happened since June when the training slots for 18/19 were promulgated and the training pathways mapped out for the S/Os who’ve been allocated a slot and are awaiting their training course.
There is now no training capacity for a new S/O to go direct to a 737 F/O course given the allocations that have just been done. Not saying it won’t happen again but if it occurs it’s unlikely to be before the first half of 2019- once those currently employed by the airline and have an allocated courses actually start them.