I see date ranges and multiple dates

Why do I see date ranges and multiple dates?

In the date list you will sometimes see a range of dates, such as 1894-1895.  This range indicates the date the mapmakers began work on the map and the date of completion. In later years the Sanborn Company issued revisions that were intended to be literally pasted over the original map sheet. In these cases the last date refers to the date of the most recent pasted correction. Digital Sanborn Maps includes versions of maps with and without these pasted corrections. Our collection, originally microfilmed from the Library of Congress' collection, includes all maps submitted to the Library through copyright deposit in their original form and a set of maps including pasted corrections that was transferred to the Library from the Bureau of the Census.  In some cases you may notice the same date listed twice for a city or listed once as a single year and a second time as the first date in a range. These two dates correspond to the two versions: one deposited to the Library by the Sanborn Company and one transferred from the Bureau of the Census, which may contain pasted corrections not on the other version. If a map is from the Bureau of the Census, an asterisk (*) will follow the date in the date selection box.

The date box may also contain an entry for "new and additional sheets."  These are updated sheets created by the Sanborn Map company intended to replace sheets of previous maps. The image of the sheet will refer to what sheet it replaces.