That's what happens with requisition numbers for jobs! If they're too short (12345), recruiters remember them, start building manual processes dependent on them, and then when they collide with others on a job board (like Indeed, or if the employer hires an agency to help) you end up needing a parallel identifier...
Lesson: if you make your IDs easily decodable, people will decode them and use them directly instead of whatever API you intended them to use.