Called WD warranty. The rep told me "if the drive was shipped, it means it had passed QA". However she also confirmed that I won't be able to return that drive if ever it fails in the future, because of that broken sticker.
WD also said that as soon as they receive any drive returning from warranty, they put it in a machine to wipe existing content. I don't need to worry about data confidentiality.
As a compensation for the unfortunate extended delay, WD agreed to send me a pre-paid label to return the drive.