Well, they both have a lower mintage than the other ones. The mintage for the 1946 is 620,734, and the mintage for the 1949 is 464,000. These are worth more and are rarer, because the mintages of the other brass threepences are in the millions - they are much higher! In Coin Yearbook, the value of the 1946 is £225 in UNC, and the 1949 is worth £250 in UNC  What book did you get the value £100 from btw?