Approximately three million German soldiers and their weapons were captured by the Sovieticon Union during World War II. The weapons were dismantled, reconditioned and reassembled. Most of them have the "crossed rifles" mark, it looks the letter X. During this process they mixed up all the parts, that's why they have a mix of serial numbers. The weapons were kept in storage and they gave them to communist forces in conflicts all over the world. They showed up in Korea, Vietnam... etc.
"Matching numbers" are important for the value of your K98kicon. An original all matching number K98k has a higher value than a mismatched number rifle.