There's a good and a bad way to look at this. Yeah, my game was glitched as well and Delvin's dialogue never came up. But even after the whole Nightingale storyline was wrapped up I pushed on and did all of the City Influence quests and was eventualy made Guild Master. At this point Tanilia offered way more gold for each eye than Delvin did for one eye. So, yeah, the Larceny Targets is incomplete, but it doesn't lead up to anything anyway. And, if it ever gets fixed in one of the patches, Tanilia always keeps both eyes in her inventory, no matter how much time goes by.