Cell References data that doesn't exist?

When I use the formula:

='2008 Apartment Comps (INPUT)'!AC27

it spits out 1/0/1900 even though the cell is blank. Where is this data coming from?

It only does this on some cells, which is why it doesn't make sense

Secondly, for the cells that are blank and don't have this problem it displays a "0", is there a way to have this not show? Like possible use an if function?

My approach was this:

=(Sheet1!C18) AND IF(A16=0,"")

but it doesn't work.