Script for InDesign to detect on which pages the threaded text frames span to.

findThreadedPages.jsx

var doc = app.activeDocument;
var page = doc.pages[0];
var page_ids = [page.name];
var text_frames = page.textFrames;
for(var i=1; i<=text_frames.length; i++){
  var text_frame = page.textFrames[0];
  var threaded_text_frames = text_frame.parentStory.textContainers;
  for(var j=1; j<= threaded_text_frames.length; j++){
    var threaded_text_frame = threaded_text_frames[j-1];
    if(!inArray(threaded_text_frame.parentPage.name, page_ids)){
      page_ids.push(threaded_text_frame.parentPage.name);
    }
  }
}

function inArray(value, array){
  var result = false;
  var i = 1;
  while(!result && i <= array.length){
    result = result || (array[i-1] == value);
    i++;
  }
  return result;
}

alert("Text frames span to pages: "+page_ids.join(', '));