I want to be sure we are in agreement on what we consider the semantics of an interval, with respect to precision.

The interval:
Doesn't really mean:  
(1) "the interval of time beginning at the first instant of 1964 and ending at the final instant of 2008".

Rather, it means: 
(2) "the interval of time beginning 1964 and ending 2008".  With YEAR precision, meaning it could have begun anytime in 1964 and ended anytime in 2008.

In order to represent (1) you'd have to have date and time on both ends, and the spec does not support date and time in an interval.

We will relax the restriction for an interval that the start and end precision must be the same.  Thus


Means "beginning in 2004 and ending in August of 2006".

(1) Does it mean that interval of time, or
(2) Is it a way to represent when an event occurred, saying "it occurred sometime between 1964 and 2008".

And my understanding is that this question is out of scope, it could be either, it is a matter for the application to specify for a given data element.