The dates are an irrelevance, though, aren't they? Every week I buy one pack of bananas which are supposed to be ripe and ready to eat (they often aren't) and another to ripen at home, and like you I've often noticed they have the same best before date. However, the bananas themselves are indeed much greener. I put them on the windowsill in the kitchen which is well away from the radiator and gets no direct sun. The 'ripe' ones go straight into the fruit bowl and are usually ready to eat by the following day if they weren't on the day they arrived. The green ones are ready to follow on within 2-3 days and are usually still edible on day 6. Works pretty well in winter. Not so easy in summer when bananas go overripe far more quickly.
It's several days on now, and yes - the date on the ripen-at-home ones has proved fairly meaningless - will stick with those! Unfortunately my experience with the ready-ripe ones isn't "ready to eat the following day" though - it's "better eat the entire bunch the following day - they won't be edible after that!"