I’ve finally gotten around to testing the 1h Strength Wrathion weapon (Faralos, Empire’s Dream) and its attached unique corruption, Searing Flames.
WCL target dummy: Warcraft Logs - Combat Analysis for Warcraft
(Please don’t mind the random rogue that decided to hit the dummies too 
)
AMR sim: Not Available
Some of my conclusions:
It looks like no matter what you do, you only get one stack per button press, even with two equipped and hitting multiple targets. This means you get one stack for pressing Remorseless Winter and Frostscythe, regardless of the number of targets hit, including 0 targets. (Note that the sim seems to get a stack for every tick, which was not happening in-game)
On the flip side you get no stacks for pressing Blood of the Enemy, Pillar of Frost, or Empower Rune Weapon. Noticeably you also don’t get a stack from using Chains of Ice, even with the Cold Heart talent.
You also get no stacks from auto attacks or procs of Rune of Razorice (there was an entry in the sim for gaining a stack based on an off-hand attack and I am not sure exactly why, these were my guesses).
It also looks like the damage stacks from two weapons rather than the application count.
In the end, this means the difference between the simulator and the log is something on the order of 400k damage over 2 minutes, assuming everything was set up correctly.
As an addendum, this is an old log from a M+ wearing one of those weapons, for completeness: Warcraft Logs - Combat Analysis for Warcraft