Yeah, it's sort of annoying.I fucking hate the shipyard. After months, the heirloom ring finally showed up on two of my characters, and the first one just failed on an 89% chance. I've successfully completed almost all of my missions that are over 80% but god fucking damn it.
Fuck you, Blizzard.
EDIT: They better make heirloom rings more easily obtainable in Legion, since no one will be doing garrison shit. Also, I fucking hate this idea of making heirlooms into time/gold sinks. They're basically punishing you for wanting to skip content you've already played a hundred times over.
Whenever an heirloom ring mission showed up for me I literally went to the vendor and bought the counters I would need just for that specific mission so I could get my chance up to like 98%. Wasted some Garrison resources, but I just wanted to make sure I got those damn rings lol.