Hi Yev,
Your two tables to have 16 groups each, but only 7 groups are shared by the two tables (10,11,12,13,14,15,16). The other 9 groups are different: 1 (study) vs 1 (test), 2 (study) vs 2 (test), etc.
Because (the space character) comes before any digit in the alphabetical order, the second possible value of group for example in the study table is 2, but 10 in the test table (because 1 comes before 2 and 0 comes before 1). So any participant running with a counter value of 2 (or modulo 2) will be assigned group 2 from the study table, and group 10 from the test table
Jeremy