WAT limits are a bit more general than that and, in particular, second segment WAT is only one of a number of separate WAT limits.
For instance, the current FAR 25 words are along the following lines -
(a)
FAR 25.119
(b)
FAR 25.121
(c)
FAR 25.123
As generally applies, the present rules don't apply retrospectively so, for any given Type, one needs to look up the relevant frozen Design Standards for the particular Certification. However, while the specific detail may vary historically the current rules give you a picture of something approximating what the story is for any recent Types.
Obstacles are quite irrelevant to Design Standards (eg FAR 25) and don't come into play until one looks at Operational Standards (eg FAR 121).