Several times I have received notices "package delivered" and then they arrive the next day or later. I think it's delivery drivers trying to hide the fact they didn't make all their stops in the recommend time.
By me, for Amazon stuff, when it's being delivered by Amazon, it is very reliable. Followed by FedEx. The times that I've gotten excuses why it wasn't delivered on time or that's its been delivered and it wasn't, is when the delivery is done by UPS and USPS. In these cases, it has always arrived the next day. I like that most Amazon delivery people takes pictures of the delivered package(s) for confirmation.