In 75 the news that Topps had a test issue spread through the Hobby quickly aided by the fact that the Sports collectors Digest was in Michigan where the Majority of the test area was. My Dad and I bought a Wax case from a Detroit dealer at a NYC show that spring which we promptly opened up and made sets
. At the time Topps said that Minis were 2% to 5% of production. And at that time a regular set was roughly $9.00 and a Mini set $25. As for the premium almost all of the Minis were gobbled up by collectors and were cared for vs the standard issue that was widely distributed and played with and enjoyed by kids like me (I was 14) Over Time with condition playing a key role almost as many nice Minis exist as regular issue Topps so supply and demand has eroded the premium.
A couple years later with 1977 cloth stickers the same thing happened collectors bought the majority of the cards and the hobby was over saturated. There are far less cloth stickers than regular issue but much more demand for regular issue. JMHO
Jonathan