Revisiting this thread (there are only 3 entries on this topic).
I ran into a similar question about when to use Triangular vs. Beta Distribution method on the Formula Study Guide (# 58 in the 105 Questions). I don't specifically see guidance to use one formula over the other in the PMBOK guide page 170 or 171. However, I do see that the Beta Distribution has, in parentheses, "from the traditional PERT technique" next to the formula label.
i.e., Beta Distribution (from the traditional PERT technique). tE = (tO + 4tM + tP) / 6
Am I to read this as -- use the Beta Distribution formula unless specifically instructed to use the triangular distribution?