Mikul,
S&B has recently changed the velocity on their 7.62x25. A few years ago, they were advertising it as around 1500fps. The website has now changed and they advertise it as being 1647fps. It sounds as if you may have numbers for the older loading.
Also, I'm curious as to where you are getting your velocity numbers for the Czech surplus. I've never seen anyone say that it was under 1500fps before your post. In fact, I've seen it reported several places that it was over 1600fps.