Some Photographers "don't exist" in User Database

I’ve noticed that some photographers who’ve uploaded some great shots (including staff picks) do not ‘exist’ when you click on their username that appears at the bottom of a photo’s page.

Examples:

http://flightaware.com/photos/view/85448-60cf4e4e8d89b2c2517ed85c71ea94b5a174b20d

http://flightaware.com/user/JNArmstrong (“No such user: JNArmstrong”)

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http://flightaware.com/photos/view/45753-e0b1c7a3256eba11674f2189d950c5ed254b5826

http://flightaware.com/user/MGiessel (“No such user: MGiessel”)

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http://flightaware.com/photos/view/455003-53b075cb74c9535c5dec8286736b201365f94e6a

http://flightaware.com/user/tengvalson (“No such user: tengvalson”)