Progressed Moon Trine Moon

Colin Hulk couldn't remember what "happened" within and without when his progressed Moon trined his natal Moon.

There could be various reasons:

• Moon can be rather unconscious. When you have double unconscious energies, it becomes hmmm even more unconscious
• Trine aspect flows. Even if something "happened", the person might not be aware of it. Plus the point above.

Arroyo states:

The most important aspects formed by the Moon as it progresses through any chart are, as mentioned before, the conjunction, square, and opposition. In addition, it is useful to note any other exact aspect , for - while such aspects do not regularly correspond to important developments - they also will be seen to "act" decisively in some instances. 

Or another view is that the "event" could have "happened" within a month before or after the exact aspect.

Practically speaking though, it might make sense to focus on the hard aspects - conjunction, opposition and square. Otherwise, there might be information overload.