I have a question about the terminology in the Timp. description in the Directory of Instruments for CoMB: "Range from C1 to C3 - hits (L/R hand round robin)"

In GPO one could produce a Timp. roll with left and right hands in separate octaves both in the Basic Orch. Perc. group and the Timp. as well as having a "double hit" option. In the CoMB Timp. it seems to be indicated that one needs to produce a roll on one key with both hands - and in practice that appears the only option, there isn't even a "double hit" KS. The two key roll option is still available in the Basic Orch. Perc group however.

Am I understanding this correctly? Why the difference? And please clarify "round robin."