Well,
you might actually get the letter earlier then an answer.
Still, I would certainly mention all your dates and as one important factor something to the effect that "if USCIS requires additional information, you are happy to provide it, but unfortunately there is complete silence on their end"
This at least ensures that you are willing to work with them pro-actively and that you want to help them as much as possible.
That way you ensure that the "hold up" is not on your end.
The point I would drive home is that USCIS should contact you with information on the delay *AND* what you can do to overcome that delay and finally I would ask for expected dates in the event nothing further is needed from your end.
HTH
