On this page I see examples of both "page" and "pages". http://www.loc.gov/standards/mods/v3/mods-userguide-elements.html#part

I would advise looking at whether there is a different context in which your contributors are using "page" as opposed to "pages."


On Nov 4, 2016, at 9:39 PM, Richard Karnesky <[log in to unmask]> wrote:

The XSD schema used to denote suggested units as 'pages, minutes, etc.'  The outline of elements and attributes still does. Chris Putnam's bibutils had to address this almost a decade ago. Postel would tell you to import both and to export only 'pages'.

Also note that we've also talked about how to represent a reference that is on a single page.  Don't know where that is now, but I remember Chris had changed bibutils to emit:
  <detail type="page"><number>3</number></detail>

rather than your example:
  <extent unit="pages">