Hi Pipzip!
Derp's twisted skull came on gradually. We didn't know it was happening until she was at least 5 weeks old, when I looked at her head on and studied photos of her I was thinking, "Gosh is her... is her skull crooked? No, it's just an illusion from the cheek poofs." ... but sure enough it WAS crooked! It's not major, but you can tell if you look at her head-on.
Thank you for the list! It's awesome, I'll use it for now since this thread is sooo long!
You may call me Kristin.

Anyway, thank you for the response! I will keep a close eye on Iddy Biddy in the mean time and hope that things don't get any worse. It's a relief anyway to read about Derp living such a happy, mostly-normal life. At least I shouldn't have to worry about Biddy suffering if her skull twists any further. (I have confirmed a very slight twist, by the way, but I have yet to get a picture that shows it very well. :/ )