Yes, the NI system works fine for me and we do get reminders 6 to 8 weeks in advance. But there are 'horror stories' out there, we all have them, me included.... here's mine.
Our Minor Traveller (and of course all other Minors) has an exhaust hanging strap bolted through the boot floor. Our car had been repaired in the past in that area and the hanging strap moved leaving the original hole. The 6mm hole had started to become ragged and no longer looked drilled. The car failed on a rust hole within 300mm of a vital suspension mounting point! I asked to see it and was shown the strap mounting hole.
I explained what it was and was told it had to be repaired as the car was now recorded as a Fail. I immediately booked a re-test - I got one the next morning. I went home, cut a postage stamp size piece of steel and welded it in place with 4 spots of MIG. You guessed it....it passed! It still has that repair to this day.