They might have gotten a few more, but the Akaviri Dragonguard was responsible for many more. Like the list mentioned, any rumors of dragons they checked out, and the dragons, if they heard/saw/realized the Dragonguard was around, left. The Dragonguard came from Akaviri hunting dragons when they met Reman. http://www.uesp.net/wiki/Lore:Atlas_of_Dragons%C2%A0%C2%A0Four dragons killed at the time of the Dragon war, and 14 killed by the Dragonguard. There were probably more killed during the Dragon war, but I'll guess recording keeping wasn't a priority then. The Dragonguard did keep records of the names they found, at least.

Remember my personal experiences with giants, ballistic trajectory plotting, and low Nirn orbit? Giants seem to not distinguish between "dragon attacking" and "random adventurer/traveller passing through". I've seen the fights, some of them I've gotten the soul, some of them I've run past because I don't like killing giants [when I'm high enough level to do it without the usual problems] Otherwise I don't like getting killed when I'm lower level. That would explain why I've gotten souls when going through an area, whether or not I found the dead dragon....

I think he took the "end of the world" too literal.

hahaha you just desribed over half my characters lol!!