Why is my version of ficciones so thin? Is this the normal version? Bought it on a thrift store.
I haven't seen that addition before, OP. Couldn't tell ya.
But Borges never wrote anything particularly lengthy, so it may very well be that's the complete Ficciones.
If you're willing to drop more cash, the book Labyrinths is all of Ficciones plus a handful of solid essays. It's my go-to book for introducing friends to Borges
If you're into Argentinian culture, his poems are pretty decent. I definitely do not recommend The Book of Sand--there were maybe two or three stories in that collection I felt were worthwhile.
I guess, if I had to give you a straight answer, The Aelph would be next.