that's still a valid address though isnt it? it's just that no one knows the priv key. That's different, here blockchain is importing a "private key" and giving you what it says is a valid address, if you edit the address it says checksum isn't valid, so that website clearly thinks that an address is valid that the other guys are saying is not, which seems to be a big flaw in blockchain.info.
It's saying
https://blockchain.info/address/1MtR9nBGfWBLY23q4dRGRjjzBBiEdxRmC3 is a valid address, and the guys here are saying it isn't
WIF private key is either valid or not. You can check yourself here, down on the page you have 'WIF checksum checking':
http://gobittest.appspot.com/PrivateKey5KZnsvrXDcP7JFD7GCuZvifrbcBtK4kAe8nHx6ibktgvPJxs4Lp should have checksum 08FA7CC9 and it has 1E157B43. Key invalid, end of story. Any wallet that imports it has a bug.
is a valid bitcoin address and i've tried a few different places. End of the day i don't really care, it's an empty address, but everywhere i check says it's valid.