OK, I have a Klefki with 4 Perfect IVs(Everything except Attack and Special Attack) and a Honedge with perfect IVs in Attack, but terrible IVs in everything else.
I originally thought the Destiny Knot passed down 5 IVs from the parent holding it, but according to various searches, Destiny Knot actually passes down 5 IVs from BOTH parents, 2 IVs from one and 3 IVs from the other(assuming the randomly chosen IVs don't overlap).
Now I'm confused, because I was IV breeding according to my previous(and apparently incorrect) knowledge of Destiny Knot, and according to a few IV calculations on some of the resulting baby Pokemon, this has been working perfectly fine.
Here's what I've been doing:
Klefki(male) holds Destiny Knot. Honedge(female) holds Everstone to pass down Brave Nature.
I thought that Klefki would be guaranteed to pass down five of its own IVs. I wanted it to pass down Def, SDef, HP, SAtk(27-29 IVs according to calc), and Speed, while the Honedge passed down its Attack IVs. I figured the fastest way to do this without calculating the IVs of every single Egg that hatched would be to see if the offspring's summary said "Likes to thrash about" which means it would have 31 Attack IVs. After calculating the IVs of several hatched Honedge whose summaries said that, I determined that this worked, the offspring had perfect IVs in everything but SAtk, and continued breeding.
If my original idea of Destiny Knot was incorrect, why did the breeding work? Several sites specifically stated that a Destiny Knot passes down 5 IVs total, from both parents.