Before February 1922, a red star on a budenovka (pointy cloth military helmet) was decorated with 5-6 mm black edging.
The mere idea of sentencing the main character to be "imprisoned" in a hotel for the rest of his life is historically nonsensical: Count Rostov is what the Soviets called a "social parasite," an individual accused of living off the efforts of others, and realistically he would've been sentenced to forced labor, most certainly not to keep living a life of a freeloading.
Count Rostov has pierced ears, which is most unacceptable for a man of his status, or any man at all of the era for that matter.