I think that "technically" we have a late talker DS too. Not sure - very odd situation. He had two words at just a year - then never said them again. Every couple of months he would add another one or two, just to forget them as easily. Until then and 17 months he said nothing. Then out of nowhere while doing a puzzle he said "no, not there." How do you go from not saying a single word to putting that together? Lol.
At 17 months, a speech therapist we spoke to informally sounded concerned, but at our 18 month appointment our pedi. said if his receptive language seemed okay (he understands EVERYTHING) and he even said just one or two things, he wasn't worried, and said to wait until the 2 year mark to look into it formally.
I can tell you that in the last week alone, he's added some words, but not necessarily fully understandable. Like he says "coo" for cookie - he just doesn't finish the word. For "apple" he'll make the "a" sound and nothing else. Not sure how normal this is. The whole language acquisition thing is fascinating to me, and I guess I'm just looking forward to him saying "mama" some day (he doesn't say that or "daddy") and just being able to communicate his needs.