Don't you love it at the end of a job, when everything seems to go wrong (Murphy's law anyone?), PM's start blaming Revit? "These notes aren't showing up! (found out later they were deleted)....These windows are not printing! (again, deleted).....9 MEP sheets won't show up in the Sheet List! That's it....we're re-typing the sheet list in a text box!".
"Wait! Did you check if the "Appears in Drawing List" parameter is checked for the missing sheets?", asks Dave. "Of course they're checked!", answered Courtney in disgust. I'm kidding, she typed it nicely :)
So I looked at the file and I found nothing wrong. I quickly created a sheet list and it reported 124 sheets. Next I linked this project in another file, created a sheet list and it still reported 124 sheets. Eventually it turned out to be just as originally expected: unchecked parameter. Hold on, there is a lesson to be learned, which doesn't involve me grinning and singing "I told you so", because that would be mean.
Now to the serious part. What happened is that when all sheets were selected and the properties box was accessed, the user observed that the checkbox was in fact checked. Now let's see if you can spot the issue:
Do you notice it's greyed out? The user thought it was read-only and so she didn't think twice about it. Unfortunately, in the world of Revit, this instance parameter is usually not greyed out and in this case it just means that some selected sheets have a different value than what's shown. In fact, you can click one time on the checkbox and it will no longer be greyed out. Now all selected elements will have the parameter checked. To me, this is a User Interface problem. Here's what we are used to seeing when selected elements have different values within the Windows OS (such as selected files with different attributes):
Ah yes, one more thing that needs improving!