You may contact Ithaca arms and they will date your shotgun for you.
Your serial number indicates that your Ithaca shotgun was made in the year 1920.
You have an Ithaca NID model made in 1926, Not knowing condition or grade 300 -3500.
If that is an old double barrel "New Ithaca Double" it was made in 1926.
1976
Its an Ithaca Flues model made in 1921
Its an Ithaca Flues model made in 1921
It was made in 1919.
612
about 1925
The Ithaca model 66 single shot shotgun that was made from 1963-1978 was offered in 12ga,20ga and 410 gauge only.
You have a Ithaca model Flues shotgun that was made in 1912 with the serial number that you supplied.With the many variations and grades made it would be better if you may have your gun appraised by someone knowledgeable in this field.
You vave an Ithaca sxs Flues model made in 1911