Over on the game's official forums, we see users reporting that they're receiving building parts for business and community building upgrades that they've long since completed, which is, of course, not the way this feature is supposed to work. These users were then asked whether or not they had actually fully upgraded the businesses they were receiving parts to, to which the answer was still a resounding "yes." The point of all of this? Special Delivery Crates may now be available to send to your friends in CityVIlle, but they (like the special delivery crates, boxes, etc. found in other Zynga games) are apparently bugged.
Let's put it this way: if you know your friend needs a very specific building material, I'd either send that particular item from the game's free gifts page, or (if it's not available), wait for them to manually request it from you instead. At least, that is, until Zynga can fix the issues that are already found with these Special Delivery Crates.
How many items have you received from Special Delivery Crates that you've actually needed? Will you send these items to your friends? Sound off in the comments.