Guy Betsy:
My partner qualified for Silver recently, and a weird thing happened. The BAEC officially started his Silver membership a date 2 days after his Silver qualifying flight. He took a flight one day after the qualifying flight (1 day before the 'official' Silver start date)...the points tracked normally and the miles tracked at 125%. Then mysteriously the points were reversed, but the miles were left intact.
We sent an email to BA and they reversed the reversal. They will do the right thing, but you may need to point it out.
PS: welcome back to the Great White North!