I've always heard about the driving after c-sec rule, but never about driving past a certain point in pregnancy... my mum always said 'just stop driving when you can't fit your belly under the steering wheel any more' and I know she stopped driving at 34 weeks because she's very petite and literally could not fit behind the wheel, but I've got really long legs so I can always reach the pedals I drove right up until the day I gave birth at 40+7 and never had problems, I believe I drove while in labour on the day (but I hadn't realised I was in labour yet, waters were intact, just had killer contractions lol).
Maybe give your insurance company a quick call and just ask, they have probably dealt with 'sillier' questions before and if it helps put your mind at ease it can only be a good thing Good luck!