Autos can be weird beasts, you cold try giving it a bit more down time and altering the light schedule to see if it will give it the push it needs. eg 12/12
I have seen this happen on another persons grow but they where doing a fastbuds Mexican Airlines plant. not a Northern Lights plant, but both are autos though. For them they waited for a bit and went from 24/0 down to 16/8 and it fix a lot of their issues then the plant started to bloom.
Are there are no pistils at all on any of the nodes anywhere on the plant? can you confirm if the packaging says its auto or photoperiod?
I highly doubt it was a mix up but always good to check, and if they where sent in little zip lock bags for stealth shipping its not impossible to be the wrong seeds,
I was once sent photoperiod vs an auto but did not know the different till a year later when I reordered the seeds and noticed a different coloured package lol. I also did not know much about growing and had them on a 12/12 light schedule from seed.
I also looked into the suggested below about averaging out other seeds flip to flower from other diaries and its about 5th or 6th week when they documented it flipped.
growdiaries.com/diaries/91650-growers-choice-seeds-northern-lights-autoflowering-grow-journal-by-kentuckyog60
this person had a bit of a late flip but not 9 weeks and the one week of veg on week 8 I would have classified as flower.
Good Luck!