I went to 42 attempting a VBAC, and in hindsight could have gone longer. Monitoring showed a healthy happy baby so there was no real "medical" reason at that time other than they were toey with me being a VBAC'er and at 42 weeks and saying that babies can die after that with no warming. Should have asked for that study.
On another forum I have read of a lady who went to something like 45 +1 with absolutely no issues.