How true-to-life was 'Joyeux Noel'?

There is a nice article about this

There are very interesting facts about this:

Perhaps the biggest misconception about the Christmas Truce of 1914 is that it was limited to the days around Christmas. In fact, fraternization had often occurred in war; it wasn’t all that uncommon for soldiers who had been shooting at one another one day to wave a white flag to exchange food or drink the next. While largely discouraged, such activities happened all the time, even under the threat of serious punishment.

About the soccer match:

“The evidence for football being played is from letters and various other paperwork from individual soldiers,” added Baker. “It gets no mention in unit war diaries, regimental histories etc and indeed some men wrote that they simply did not believe that it had taken place.

“The circumstances of the cratered nature of the ground, presence of barbed wire defenses and so on, plus the very short time over which fraternization occurred, make it most improbable that we are talking about a properly organized game,” Baker suggested. “A kick-about is probably nearer the mark. The only place where even two British reports mention football was on the front of 15th Infantry Brigade, but no corroborating German evidence from that sector has been found.”

And some factual mistakes are listed here:

A very common error in First World War films. British soldiers were not permitted to shave their upper lips until 1916 - in 1914 almost all (unless physically unable to grow them) would have had moustaches.

In the scene right after the couple sings, they mention that they first met five years ago, in Oslo, Norway. However the city had been known as Christiania since 1624, and was only changed to Oslo in 1924, after the time period of this movie.