thats where is the RD and ND comes into picture
if you have mailed an application on 2/4 then INS will have ur RD as the date they recieved it say 2/5 or 2/6, then it is sent to the dept where the application is entered into the system and your check is sent for cashing which is your ND. But the RD is the one that matters for processing. I saw this information on the VSC web site.
And why it took so long for your check to be cashed ? - maybe INS had more mails during this period, I saw some TSC\'s posting stuff around feb 14th about their cases transfered to VSC.. I am not sure if thats the reason.
hope this helps.