I think I've fixed it. Reuploading now. Bear with me.
The problem was a fairly stupid one. I edited the assert to fit P5200 instead of P5210 (I'm using the same updater-script I used for the wifi model stock kitkat).
Problem is, I used mac textedit instead of gedit. One preserves linux encoding, the other does not. Can you guess which is which? :P
I believe it was Homer Simpson who said, "DOH".
Anyway, edited the updater-script with gedit and just removed the assert completely, so once it's done uploading you should be able to flash without issue.
Death to all but metal.
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