those kinds of -PNA/-EPO/-NAO patterns can deliver good overrunning while the block is in place and the TPV is close. likely have Arctic air over the top
at the same time, i think the lack of retrogression on the GFS is due to the fact that it buries everything out west and you don’t have that final wave break
i think the GFS just buries it. doesn’t mean that it’s correct. even if it is correct, it just delays the cold air outbreak for a few days, it wouldn’t be disastrous or anything