<p>First, it's likely that your teachers' letters are actually at MIT, but that they're sitting in a pile somewhere waiting to be sorted into your application. </p>
<p>Second, even if there is some problem with the letters, you can have your teachers re-submit them after MIT is done processing all the mail -- no worries. </p>
<p>From Matt McGann's blog, here:</a>
It is perfectly fine if, through no fault of your own, your school forms (e.g. teacher recommendations, secondary school report, transcript) come in after the January 1 deadline. We are much more understanding of and flexible with late documents from schools than with late documents from the applicant.
The MyMIT Tracking is up-to-date (while the Admissions Office is closed, the Records Office is working hard), but please recognize that processing can take 2 weeks. You do not need to worry at this time about documents that are not showing on MyMIT; we currently have a backlog of materials in our processing center, and expect to have that backlog into January. Do not send a second copy of any document at this time. Also, you do not need to call MIT Admissions at this time to check on any such documents (there is a time for this later). Do not worry about materials that have not yet shown up on MyMIT Tracking.