How to Prevent Users from Reverting to Old Version of Google Spreadsheet

With the code below you can have a fairly responsive interaction with the user.

Code

function onEdit(e) {
  // allow book name to be added
  var cell = e.range.getA1Notation();  
  if(cell == "A7") {
    return;
  }

  // only if conditional color is present
  var color = e.range.getBackground(); 
  if(cell != "A7" && (color == "#cfe2f3" || color == "white")) {
    var first = e.range.offset(-1,-1).getValue(); 
    var second = e.range.offset(-1,0).getValue();

    // first entry
    if(typeof first == "string" && second == "Current") {
      return;
    } 

    // non consecutive weeks
    if(typeof first == "number" && typeof second == "string") {
      respond(e, "Not consecutive enty !!");
    } 

    // out of range  
    if(first == "") {
      respond(e, "This entry is out of range");
    }
  } else {
    respond(e, "Out of bounds");
  }
}

function respond(e, text) {
  e.range.clearContent();
  e.source.toast(text);
  return;
}

Example

I've created an example file for you: Copy of Reading scheduler. See also revised code for removing data.

With formula's it can't be done, as per your other question, but with a little piece of Google Apps Script you can roughly accomplish what you want.

Code

// global
var app = SpreadsheetApp.getUi();

function onOpen() {
  // create menu entry
  app.createMenu("IDs").addItem("Set all IDs", "myIDs").addToUi();
}

function myIDs() {
  // set variables
  var sh = SpreadsheetApp.getActive();  
  var rText = app.prompt("Give range", "Like A1:A10 (single column only)", app.ButtonSet.OK_CANCEL); 
  var r = sh.getRange(rText.getResponseText()), v = r.getValues(), max = 0;

  // retrieve max value
  for(var i = 0, iLen = v.length; i < iLen; i++) {
    var value = v[i][0];
    if(value > max) {
      max = value;
    }
  }

  // prepare output
  var output = [];
  for(var j = 0, jLen = v.length; j < jLen; j++) {
    var val = v[j][0];
    if(val == "") {
      output.push([max + 1]);
      max++;
    } else {
      output.push([val]);
    }
  } 

  // show/return results
  r.setValues(output);  
}

Explained

From the menu, the script is activated. A prompt is shown and a range is requested. The script will retrieve all data from that range and find the highest value. Afterwards it will evaluate the range for empty entries. Once found, it will add a value (max + 1) to that position and re-set the maximum value. At the end of the script all data is added new data to the spreadsheet.

Screenshot

before & after

Example

I've created an example file for you: check if cell itself is empty
Add the script under Tools\Script editor from the menu. Press the bug button to authenticate the script.