If they used a mail-merge program or something similar to print the labels (something which is very common) errors can easily creep in if the person feeding in the data does not correct for commas or other punctuation which denotes field breaks. At that point, one can end up with incomplete addresses.
And, of course, if something is widely popular it can overwhelm people - Reaper suffered the same sort of thing, I think, with their Bones kickstarter. Their problems weren't that people didn't get KS stuff - rather, the KS-designed models are taking a while to reach general release.
Which is fine, because I have enough to paint as it is!