I just got back after a couple days away. Thanks for the bouncing answers, and even greater thanks for the discussion that followed. Fascinating!

Not to belabour the matter, but back to those famous rubber baby buggy bumpers for just a sec. I know the babies aren't rubber. Not sure if this got pointed out, but it's possible that either the bumpers alone are made of rubber, or the entire buggies are. I think that is the ambiguity (even with a basic understanding of babies, buggies and bumpers) that is hard to correct with hyphens.