Casting Surface Finish

One thing I noticed about the first cast iron that I purchases I made last week and this weekend is the difference in the cast surfaces of the different pieces. The 1950s #3 lodge from last weekend and the #5 & #8 BSR skillets from this weekend all have extremely smooth outer surfaces and a very fine "grain structure". The inside cooking surfaces are almost mirror smooth now that they have been cleaned up. They are noticeably different then late #3 Wagner and Late #8 Griswold (when owned by Textron) that I purchased. They have a much courser outside surface even though the inside surfaces on both are mirror smooth. I was wondering if older pieces are always "finer" made? I am sure cooking will not be different on any of these once they are properly seasoned.