Split scales
 

The umbilical scar is short and not deep. By your photo, this is not an umbilical scar. It is too deep and too many scales are involved. Take a look at my pic on my thread on an eastern indigo with a red throat. The problem is more common in indigos with red throats; I do not know why? Could it be that breeders are trying to get a more intense red throats and breed related lines?? On your snake I would bet that if it is in an arc/bend in that area that you would see these scales independent of each other and this splint will be very noticeable . If it does this you do not have an umbilical scar. Take a look at my pic. Even though the seller said it was an umbilical scar and that I would not find better, I returned the red throat eastern indigo. I was glad I did and I learned a valuable lesson. Aberrant scales are one of the first signs of inbreeding. Alan Brutosky and east coast drymarchon can help answer some of your questions. Was this snake the first clutch this breeder hatched out; indigos?

Alan knows his stuff. No doubt about that. But in my opinion the umbilical scar is also shown here. If not, where the heck is the umbilical scar? It may be within the long scar shown here. Those scales are in the proper location to be an umbilical scar. In a neonate snake, it has to be somewhere.
I am not debating the problem with inbreeding indigos, nor am I defending the seller who sold you the indigo you returned. But what evidence do you have that this problem is more severe in red throat indigos? And yes, I know all about Bruce's attempts to produce brighter red throats, and the subsequent inbreeding disasters.

indigo
 

I have no evidence that the defect is more prevalent in red throats. But it is mentioned more in the red throats.

I think we agree that inbreeding is an issue with couperi, and it will get worse until Alan and his guys are successful in establishing a group of unrelated couperi. I do not know of anyone else who is even attempting this. The split scales are all we got to determine degree of inbreeding. I have seen a few in which virtually every scale was wanky, from severely inbred animals. Unbelievable. I have several couperi with a single scale or two being imperfect. You gotta look hard to even find them. I have one absolutely perfect male. But I also have one female with badly split scales in her heart region. She will never get bred and was essentially gifted to me.
I am eternally grateful I purchased the group I have. With so few breeding adults in the captive gene pool, I suspect the situation has gotten worse since I bought my most recent one in 2013. I feel for your friend and hope she is able to locate some perfect scaled babies. But it is not easy.