I think there are differences between "Authorized Distributors" and other "normal" Re-sellers (which are of course an integral part of the channel up 'til the product reaches the end- user).
If there's a Certificate of Authorization issued by the manufacturer to his direct distributor, I guess said manufacturer must have to "care" at least, if not "honor and respect" their oficially issued letters. By "caring" I mean: i.e. giving discount prices that can assure his dealer "X" amount of margin even if the price is lower online at Amazon, partnering with them for roadshow events, helping with marketing funds, train/incentivize the distributor's sale staff, etc. etc...
If the manufacturer really honors in practice the EXCLUSIVE right for sole distribution (which is not the same as mere "Authorization for Distribution") in a region or not (or else finds a parallel partner in the same geographical area to make them compete with one another) well that's another topic. In the case of "Re-sellers" there are NO letters issued to them as far a I know. I've never seen cases where distributors holding a manufacturer letter re-issue letters down the channel.
That said, I've seen some letters with expiration dates, others without. Undoubtedly, putting a date may be the fairest, just and objective way thing to end things for both, I guess.
If the "manufacturer-dealer marriage", so to say, goes well the letter gets re-newed without a problem, if not; well the letter says clearly we shall end this on "X" date.
AXIS's letter: "Authorized Partner" in the Axis Channel Partner Program with issued date but no expiration.
PELCO's: Confirm AND Certify "X" company as an authorized dealer, valid until "X" date.
DAHUA: Authorization valid until "X" date.
HIKVISION: Valid through "X" date.
Not for IP cameras, but funny that CANON seems to have an "Empowered Partner" Certificate (whatever that means) certifying their partner to stock & sell their products ...