I've specifically tested the "last hit" thing on swords from gardosen for 3rd job. Every time I would intentionally not get the last hit, I wouldn't get the item. Every time I got it, I got the item. These tests were done over all of my 3rd jobs, and it always works this way.
Some of the rumors are real, and others aren't. KOG definitely makes weird systems sometimes. The 10 fire golem hearts or whatever they were you need for 3rd job also were always a 100% drop until the 10th, which only came from one specific golem. No matter how long you tried, no other golems would drop it. Not sure if it's still that way post-revamp as I've not played in months.
As for Gaikoz's swords/seals, there don't seem to be any tricks to them.