Honestly, it doesn't make a whole lot of sense to me why anyone on that ship would get promoted. There's nowhere to go. No one is leaving that ship for a very, very long time. If you kept giving promotions to everyone who deserved it*, how many years would it take until it was a ship crewed almost entirely by Lt. Commanders?**
*Still not Harry.
You remember all the dead people who had jobs that still needed to be done?
Worf got a promotion when Tasha died, and then he got another promotion when Data briefly died in season 6 or 7.