Once I succeeded in registering, I want to thank you for your interest in the topic!
I would like to apologize for any mistakes in translation from Bulgarian to English.
I see you are familiar with the books of Dimitar Nedyalkov. Without wishing to offend the author, I dare say that they are full of inaccuracies.
For example, in the book “Bulgarian Fighters”, under the photograph of Nieuport 4487, he writes that he is 24bis.
In another book, “The Air Power of the Kingdom of Bulgaria”, under the same picture claims to be of Type 27.
Another I would say is a great inaccuracy, the circumstances of capturing of A.W. Fk3.
According to the author, this is O’Douyer’s plane shot off Balan and Uzunov, commander of 17 squadrons. Indeed, O’Douail’s plane is B.E.2c ‘4574’.
I have a picture of Nieuport 24 bis 4487 who has crashed, so the conclusion in Nedyalkov’s book is also wrong.
But let’s get back to the topic. I own a picture of Bulgarian soldiers around Nieuport 12, where the identification sign of the body is a red ring around a white circle.
As far as I know, R.N.A.S. fly with such a sign for a certain period of time.