Imessage delivery status? #iphones?

My imessage doesn't say that a message is "delivered" like it usually does… Does that mean that either the receiver or sender does not have internet? Or has it actually sent it and is just not showing it?

It must mean that the other person isn't able to receive the message, and they'll see it once they have signal/internet on their iPhone/iPod.

I have a iphone4s and a i phone6 both using same apple id. I sent a imessage to someone and my iphone 6 never delivered but the iphone4s did i thought i may ne blocked but the last time this person blocked me my iphone 6 would say delivered but the iphone 4 wouldn i'm confussed! Please note i'm not a pest this person blocks for no reason at all other than control!)