The Garrison Mission Reward Rule of Probability: The actual probability of obtaining a reward that you really want sharply decreases as the limit of displayed success percentage approaches 100. So if say, the game says that you have a 92% change of obtaining an epic trinket. The actual chance of success is probably closer to LOLNOPE at best. This rule is particularly true for epic rewards of iLevel 645 or higher.
*Sigh* I was really looking forward to that trinket. Oh, out of 14 missions completed, zero salvage crates were received.