How many SDF-#'s are there? From my understanding, there are three SDFs:


The SDF-1 which was the major focus of the first season.
The SDF-3 which is the flagship of the Robotech Expeditionary Force (REF), where Rick Hunter is.
The SDF-2 I wasn't too sure about, as at first I thought it was a separate ship built, but it was apparently destroyed with the SDF-1 in the final episode of the first season. (Not entirely sure if it's a separate ship or the repaired SDF-1.)


However, in Episode 78 ("Ghost Town"), the communications from the REF were coming from the SDF-4, so I'm wondering: How many SDF-#'s are there, and are they all the same as the SDF-1 (minus the aircraft carriers which were just a patch job)?
The Robotech Wikia has a list for SDF-1, SDF-2, SDF-3, SDF-4 and SDF-7. It includes a listing for SDF-M, but I don't think that was in the TV series (it's mentioned in the Robotech comics). Wikipedia also has a list of Robotech vehicles that has a lot of detailed information of 1-4.


SDF-1: Robotech TV series
SDF-2 Megalord: Robotech TV series (starting from episode 26)
SDF-3 Pioneer: First appeared in "Crystal Dreams" promo and in the Robotech II: The Sentinels series
SDF-4 Izumo/Liberator: Last episode of the original series
SDF-7: Robotech II: The Sentinels novels 
SDF-M: Invid War: Aftermath comics


The SDF-7 was a Horizon Class T ship, so it's not like SDF-1.