Having served as a naval officer back in the 70's, I have a slightly different take.
I don't believe Kerry ever officially had a "Less Than Honorable" discharge, but he could have been quietly under investigation by a Navy board of inquiry for his anti-war activities, with the threat of such a discharge hanging over his head. Especially after the POWs came home in '73, I could see a board investigating Kerry (especially his activities' effects on POW treatment) dragging on for years. It took a fair amount of time to fully debrief the POWs. In addition, there could have been a very interesting behind-the-scenes' tug-of-war going on between folks in Nixon/Ford administrations and Kerry's powerful Senate backers, who were grooming Kerry for higher office. With the Pentagon and Navy Department in the middle...and Kerry keeping a relatively low profile. When Carter took office in 1977, the board was probably directed to close up shop and drop the case. Kerry's February 1978 discharge resulted from this. Carter's amnesty program provided an additional convenient smoke screen.
I wouldn't be surprise is there were some documents in Kerry's service record concerning the board - the reason why Kerry won't sign the 180. Knowing how navy boards operate, there is interesting and potentially very damaging information contained in the board's proceedings. Certainly not stuff a presidential candidate wants released a couple of weeks before an election.
I wouldn't be surprise is there were some documents in Kerry's service record concerning the board - the reason why Kerry won't sign the 180.
That is also a very plausible scenario.
It explains the late 1978 discharge during the Carter Administration and also explains why Kerry has no intention of signing his Form 180.
But, the "Less Than Honorable Discharge Theory" is also plausible so you can take the Good Cop role and I will take the Bad Cop role. ;-)