The checker (unfortunately) is more accurate than the simple exchange maps/lists, when you give it your phone number. The address checker may be accurate, but the postcode checker definitely isn't as accurate.
Like you, my exchange is now live, but my cabinet isn't due until March 30th (nor ADSL2+ until March 31st). Just before Christmas, the date was changing on almost a daily basis - from March to December, then to March, December, June, December and back to March again.
It is frustrating to watch the other cabinets go live, when I know ours was installed and powered up at the same time as those cabinets...