ISTD syllabus is sometimes confusing because last step of a figure is sometimes the first step of the following figure.
however, it normally happens on the figure man ending OP and CBMP. it's a good way to remind you.
if you are TOO familar with the IDTA syllabus only and are required to give the feet pos. of outside change into a Nat. Turn. in this case, u may fall into the trap that forgetting first step of Nat. Turn is in CBMP OP.
for non OP ending figures like any feather finish ending figures in foxtrot. ISTD are also one step more. the objective is to show the lowering is taken as next "extra" step. e.g. foxtrot rev. turn. "lower e/o 6" means the lower is taken as step 7 is taken. there is no step 7 in IDTA. IDTA interpretor may "drop" on step 6 before next step is taken.
IDTA is convenient in precede and follow while ISTA is good in reminding u the technique.
my point is that both syllabi have strenght and weakness. and u need to understand well.