I stand duly corrected. Where is the small tire you speak of, Bill? I still don't see it. This example of a British plate from http://www.autogallery.org.ru/m/nomerc.htm sort of led me in the wrong direction. Re-reading it I now see that was only prior to '31 (I think-It's translated from Russian):
1931-1963: three letters from the ASV to YSV and up to three digits before 1931: two letters and up to four digits of the number previously unused (it looks like a series of SV).