No Clearance: Missing information

I randomly decided to send an email to one of the medical screening assistants just to triple check that our documents had arrived, which they did on the 15th of November. However, they send our a letter on the 23rd of November requesting missing information--which as of the 13th of December has not arrived!

What could possibly be missing? And why weren't we advised of this missing information in more timely fasion?

We could have left for Thailand and they could have been waiting us for to fill a request we weren't even aware of. I became quite upset this morning at the thought of missing our invitation deadline, which is March 21st.

We return from Thailand during the first week of March...cuttin' it close!