Sally Bruckheimer <sallybruc@...>
"I start by looking for a naturalization. Because if one exists, you'll learn exactly when and where the person arrived, and, for later arrivals, under what name."
This is true if the immigrants arrived late, and in a port with Certificates of Arrival. If the immigrant arrived before, say 1920, nobody checked, and everybody guessed - and the name is a mystery. Maybe they remembered it was cold, so it must have been January (wrong, maybe March or November). Maybe they remembered the name of the ship and got close: I once looked for the Rhineland, and it wasn't there, the Rheinland, however, was; this is where it is good to have a list of ships arriving in some month or sounding like something.
On the third hand, if they naturalized really early, it says nothing about a ship, just Mr. X gives up allegiance to the King of ____.
And if, like my grandfather, he came early (June 1881) at some port unnamed, nobody can find any passenger list because it disintegrated or he walked across the bridge and nobody cared to make a note.