Do people read, for example, "Bears' 20-12 loss" as "Bears' twenty to twelve loss" or "Bears' twenty twelve loss"？
There are plenty of ways. Let's assume that, from your example, Bears is one team and Tigers is the other. The Bear are winning and the Tigers are losing.
- The Bears are winning twenty twelve
- twenty twelve, Bears
- twenty to twelve, Bears are winning
- twenty twelve, Bears are in the lead
- Twelve twenty, Tigers are losing
- The Tigers are losing twelve to twenty
Or something like:
- The score is twenty twelve, Bears are winning
- the score is twelve to twenty, Tigers are losing
Whenever you mention the score, it is normal to say the name of the team that is winning.
Here is reference to Football scores