It seems Ran has seen the face of kaitou kid and confused it as of shinichi

[Dconankun]

In the first appearance of kid in DC, Sonoko asked Ran whether she saw the real face of kid. But Ran looked troubled and sad but in next panel she saw kaito and blushes and says i am glad and " I get it, I get it. " I think she misunderstands and considers shinichi as kid

[Tsukiko]

No, it means that Ran is glad that she was mistaken when she assumedly saw Shinichi in... Shinjuku chapters previously. Ran has not seen Kaitou Kid's face. The plot point when she thought Shinichi to be Kid was only in Movie 14 which was years later from this scene.

Considering that Kaitou Kid is just a visiting character occasionally it wouldn't make plot-vise any sense for Ran to think him as Shinichi constantly. Especially when Kid has never disguised as Shinichi in manga, it's only a movie thing.