Joined correctly
Before sign-in
Page viewed
Product opened
device_id: dev42
After sign-in
Plan selected
Purchase made
device_id: dev42, user_id: usr-7
One user profile
All four events
One journey
user_id: usr-7
same device_id
Split by mistake
Anonymous profile
Page viewed, Product opened
device_id: dev42 (orphaned)
Signed-in profile
Plan selected, Purchase made
new device_id: dev99, user_id: usr-7
device_id replaced, no join