I would do it in this way:
// Your settings
// ---
var SEARCH_PATTERN = '2013';
var CHANGE_PATTERN = '2014';
// Set SEARCH
// ---
app.findTextPreferences = app.changeTextPreferences = null;
app.findChangeTextOptions.includeMasterPages = true;
app.findTextPreferences.findWhat = SEARCH_PATTERN;
app.changeTextPreferences.changeTo = CHANGE_PATTERN;
// Variables
// ---
var allDocs = app.documents,
nDocs = allDocs.length, nFounds = [], counter = 0;
// SEARCH ONLY MASTERPAGES IN ALL OPEN DOCS
// ---
for ( var i = 0; i < nDocs; i++ ) { var curDoc = app.documents[i], mPages = curDoc.masterSpreads.everyItem().pages.itemByRange(0, -1), target = mPages.textFrames.everyItem().paragraphs.everyItem(); target.changeText(); nFounds.push(target.changeText().length);
}
app.findTextPreferences = app.changeTextPreferences = null;
for ( var i = 0; i < nFounds.length; i ++ ) { counter = counter + nFounds[i];
}
alert( counter + " expressions have been changed." );
– Kai