Yes, absolutely. Even in my example in the sibling comment, when I look at the first citation(s) in that paper with no date, I see: "[Cha82][CAC+81][BCKT89][Ber73]".

Great, so I guess I at least know that it must not have been published before 1989... (before I just search for the title on the web, in the hopes of finding a journal it was published in).