Montblanc marks its ballpoint refills with a month and a year. Precisely what this signifies has never been settled; it is generally taken to be a date of manufacture or a best-before date, and certainly not an expiry date after which the refill becomes unusable. The company's inks carry such a date too, even though experience shows they keep unchanged over very long periods.
In practice that means a refill can be written to the last without hesitation, even if the printed date is long past. Only when the ink has dried out and the line is no longer even does it need replacing. Age alone is no reason to discard a refill that still has ink in it.
For dating a pen, on the other hand, the refill date is useless. Refills are consumables and get changed several times over the years, so they are routinely younger than the ballpoint itself. To establish the age of a piece you have to go by the model number, the engraving on the clip and the style of the fittings.