Wait, it's ending? Always felt like this is one of those that could go on for a while longer. Well, at least it'll close on a happy note, no unnecessary drama or stupid shithousery.
Looks like every volume ends in a 描き下ろし (which Jisho translates as "newly drawn artwork", but is actually an extra chapter in Vol.1 (19.5), so not sure for other volumes), and then there are "Features"(長編): 1-6 in Vol.3 (1-4 are chapters 38.5, 40.5, 40.6 and 41.5, respectively, i believe), 7-10 in Vol.4, 11-13 in Vol.5, 14-16 in Vol.6, and 17-19 in Vol.7 (so, it's Features 18 and 19 that are left).