Census question

From an ABC News article on April 1:

The federal government calls today National Census Day to mark the deadline for sending in your census questionnaire. It's not a hard deadline, though, and the government continues its publicity push to encourage more participation.

So far, of the 134 million forms that have been mailed to households, more than half have been mailed back. Today, cities across the country will hold rallies to encourage the rest of America to get its forms in.

The form specifically asks how many people are living in your household on April 1.  If I had sent it in on the day I received it, and then one of my friends fell on rough times and I offered them the spare bedroom, wouldn't I have (unintentionally) committed perjury?  If they wanted to know how many people were living in my home on April 1, why would they encourage me to send it in prior to that date?

I've read there is a penalty for providing false information on the Census, but I've also heard people are rarely prosecuted.  But still, do they want honest answers or did they want me to make it convenient for them?

~~Code Monkey