But the fact remains, Kristjansen is/remains unbeaten in 10 outings and the three years since that setback to Zoff."
Would this work for you, David or would you still be looking for "the 10" in this situation?
A speaker (hopefully) structures his sentence to convey his meaning clearly. This commentator is giving information. Let's start by being clear what this information is:
The team lost to Zoff.
That was 3 years ago.
Over that 3 years, they have played 10 games (outings) and won.
"...unbeaten in 10 outings and the three years since..(they were beaten by Zoff)."
This could mean: in the ten days after they lost to Zoff, they played 10 more games and won. They have played no more games since then. That was three years ago; and so of course, they remain unbeaten.
The meaning that is intended is: Since that game when they lost to Zoff, they have played 10 more times over a period of three years and have not been beaten in all that time.
In the original sentence, the inclusion of 'the' before 10 outings means that of all the games this team have played in their sporting life, we are referring to the 10 games since they played Zoff. As you point out, 'the' before 'three years' would have the same implication.
The original sentence is 'commentator talk' - and depending on how 'gentlemanly' the sport, correct grammar might be regarded as 'prissy' - a bit like saying, run along and play football but don't get your nice white shorts dirty now! Fans 'read in' and give a sentence the intended meaning even when the words uttered don't.
What we have been doing is looking at it grammatically!
What I would have said is:
"But the fact remains, Kristjansen is unbeaten in 10 outings over three years, ever since that setback to Zoff."
or ( and more of a mouthful)
"But the fact remains, Kristjansen is unbeaten in the 10 outings of the past three years, ever since that setback to Zoff."