One thing that always confuses me is that for the office, all of the psalm tones, besides the tenor and meditation,all have different multiple endings. This is differentiated by the numbers and letters that follow them (eg, tone 1 D is tone 1 with the D ending, while tone 1 D2 is tone 1 with the D2 ending, etc.)
Well, the second tone is usually listed as "2.D". But, there is no other ending. It's not like tone 8 where there's two endings, (G, G* and C) Os the sixth, where there's only one. It's listed as "2.D" as if there were some ending other than the D. I wonder why that is?
Some day, I'll have to ask a chant scholar.