PetahW, that is exactly what I thought. But, I am really confused now because...
http://www.ithacagun.com/pdfs/serialnumbers.pdf
That document lists serial numbers for the Lefever Nitro Special. They are all SIX digit serial numbers. My gun has a FIVE digit serial number.
The only note I see to explain this is this, at the bottom right of the second page of that document:
"Lefever guns numbered under 100000 are guns built by the old Lefever Arms Company once located in Syracuse, NY. This company went out of business around 1916. "
Does this mean that this is a 100 year old gun?