Well I felt like I've had no luck in this game as I've not had a single legendary engram. Earlier, when patrolling Earth for a bounty I stumbled upon a loot chest containing 2 rare engrams and a legendary. 5 mins later, another loot chest with two rare engrams. I turn them in and then get levelled up to crypt arch level 3 and get another two engrams, and I've suddenly jumped from level 23 to almost 25.
It can be incredibly frustrating at times though!
Nice, but I wouldn't worry about legendary engrams until after the patch, as you're not missing much. To date every legendary engram I've had has decoded to a rare item. Thankfully they're 'fixing' it in a patch.