Key ingredients for classic Sauce Bolognese (Ragù Bolognese)? What are the ingredients, both main and optional, for a classic Ragù Bolognese?

I tried getting an answer to this question. First I looked around this site. I found one question about a "secret ingredient", a specific question about the type of meat, and a good question about flavoring the sauce with spices. I also tried making my search query more specific, but no dice.

After that I looked at Wikipedia's Ragù Bolognese article, which does contain a certain list:


  
  Ground meat (beef or veal, sometimes pork)
  Onions
  Celery
  Carrot
  Tomato paste
  Wine
  


This is only a basic list, e.g. Pancetta's missing, even though it's mentioned in most recipes. Other recipes ranked highly in Google (bonappetit.com, foodnetwork.com, epicurious.com, and for fun BBC even chips in etc.) mention several others as well:


Regular olive oil
Extra-virgin olive oil
Butter
Tomatoes (fresh, or more often: tinned or "tin crushed")
Pancetta (sometimes even bacon, but I guess that's just a inferior alternative?)
Wine (both Red and White get mentioned)
Stock (beef, chicken, as well as veal get mentioned)
Ground pepper (usually black, sometimes white)
Milk
Garlic
Cloves
Basil
Bay Leaves
Oregano
Parseley
Nutmeg
Sugar
Cinnamon


A certain related site also has a similar question that lists a subset, but without any references, explanation, historical background, or whatsoever.

So, to reiterate, my question is: what are the ingredients for Bolognese sauce? What are the staple ingredients, and what are the additions made by chefs over the years?
Italy is very protective of its food heritage and there are many examples of recipes being officially codified by various authorities, e.g, the EU designation, Traditional Speciality Guaranteed, was applied to pizza margherita in 2009 and strictly mandates the ingredients that may be used. 

The recipe for Ragu alla Bolognese doesn't have the weight of the EU behind it but in 1982 the Bolognese chapter of the Accademia Italiana della Cucina did produce an official version and it is on their website, unfortunately only in Italian. Using Google translate you can see that the required ingredients are:

Lean minced beef, pancetta, carrot, onion, pureed or peeled tomato, dry white wine, whole milk, beef broth, olive oil or butter, salt, pepper, cream

I'll leave the translation of the instructions as an exercise for the reader lest I be accused of posting a recipe. ;-)