Rowland Brooks found the first SPSS of order 38 (4920A). This discovery was published in 1950 by Tutte. At the time it was the lowest order SPSS known. P.J. Federico also constructed one (1620A). Ian Gambini found 2 (550A, 749A) with his programs in the 1990s. James Williams found 205569 new SPSSs in early 2013, Milla and Anderson found 52 later that year, Brian Trial found 237 SPSSs in early 2014.
It is estimated that there are approximately 4.65 x 10^7 SPSSs in order 38.