So, I'm reopening the debate, this time with a poll.
Do we think Chakotay held the (albeit provisional) rank of Lieutenant Commander or Commander?
I think it is Lieutenant Commander:
1. The provisional rank device has two solid gold stripes and one black stripe, apparently equivalent to the two solid and one black pip of a 'regular' Lieutenant Commander.
2. Although Chakotay was never referred to as 'Lieutenant Commander', 'Commander' is commonly used as a short form. Additionally, until Tuvok's promotion, Chakotay was the only officer aboard who was a Lt. Commander, and so with no full Commanders aboard, it was not really necessary to use his full title.
3. We have seen first officers of smaller Starfleet ships holding the rank of or equal rank to Lieutenant Commander. Lt. Cmdr Cavit, for example. Similarly, Major Kira. Major is equivalent to Lieutenant Commander in the US and Commonwealth armies, so it is likely the writers intended it to be the same in Deep Space Nine.
4. After noticing Tuvok's costume error in Season 1 (he wore the insignia of a Lieutenant Commander for several episodes), the creators corrected it by giving him Lieutenant's pips. They also changed Torres and Paris from Lieutenants to Lieutenants (j.g.) As they did not alter Chakotay's insignia to that of a full Commander, we can assume they intended for him to be a Lieutenant Commander.
Do we think Chakotay held the (albeit provisional) rank of Lieutenant Commander or Commander?
I think it is Lieutenant Commander:
1. The provisional rank device has two solid gold stripes and one black stripe, apparently equivalent to the two solid and one black pip of a 'regular' Lieutenant Commander.
2. Although Chakotay was never referred to as 'Lieutenant Commander', 'Commander' is commonly used as a short form. Additionally, until Tuvok's promotion, Chakotay was the only officer aboard who was a Lt. Commander, and so with no full Commanders aboard, it was not really necessary to use his full title.
3. We have seen first officers of smaller Starfleet ships holding the rank of or equal rank to Lieutenant Commander. Lt. Cmdr Cavit, for example. Similarly, Major Kira. Major is equivalent to Lieutenant Commander in the US and Commonwealth armies, so it is likely the writers intended it to be the same in Deep Space Nine.
4. After noticing Tuvok's costume error in Season 1 (he wore the insignia of a Lieutenant Commander for several episodes), the creators corrected it by giving him Lieutenant's pips. They also changed Torres and Paris from Lieutenants to Lieutenants (j.g.) As they did not alter Chakotay's insignia to that of a full Commander, we can assume they intended for him to be a Lieutenant Commander.