Content Generation For A New Generation
The order in which they were placed doesn't matter - if Red and Yellow both have the same number of thieves on the road, they both score the full number of points.
From the new edition rulebook:
If there are multiple meeples in a single scored feature, the player with the most meeples is awarded full points and all other players receive nothing. When more than one player have the most meeples in a scored feature, the tied players all score full points.