TomCan...I'm sorry but I have to ask what your genetics background is because as I've been reading your posts I've noticed myself cringing at the way you explain things. You present yourself as an expert...or at least knowledgable individual...yet your explanation of genetics isn't at all scientific....you use "always" and "all" when there are other possibilities. And in genetics there are often exceptions...
For example Long Coat versus Short Coat if it's a simple dominace this is what you get...
So, CCxCC= all CC or short coat
CCxCc= all short coat, 50% will be carriers for long coat
CcxCc= 25% short coat CC, 50% short coat Cc (carriers for long coat), and 25% long coat cc
CCxcc= all short coat Cc (carriers for long coat)
Ccxcc= 50% short coat Cc (carriers for long coat), 50% long coat cc
ccxcc= all long coat
Of course percentages are based on a large population so in any litter you may or may not see these results.
The simple answer is if there were any long coats in your short coats ancestry you could get a mixed litter of long and short (like Mia said). My Charlie is a long coat and came from a short coat dad, and long coat mom. I've heard of coats that were in-between long and short which would most likely mean that there are other genes that play into the coat length. (probably not a co-dominance thing otherwise it would be more common) It's kinda like eye color, brown is dominant over blue but there are lots of shades and green and hazel in the mix, not many things are as simple as dominant or recessive unfortunately.