There are really two separate issues here:
authorized dealers (ADs) and
authorized repair centers.
1. Authorized Dealers
About 15 years ago, my local Omega AD (who also carried Longines and Tissot) told me their Omega account was being cancelled because their sales volume was too low. The couple who owned the shop retired shortly afterward. Meanwhile, other ADs in our city continued selling Omega because their sales volume was strong enough to maintain the account. Their sales staff also receive brand training directly from Omega.
2. Authorized Repair
Swatch Group (which owns Omega) does not sell parts to the general public. However, Omega does allow independent watchmakers to apply for certification, receiving certain training and meeting certain standards to become authorized repair centers with access to genuine parts. The idea is to maintain a consistent, high standard of service across the board.