When did HP retire their two-shot molded keys?

[Didier Lachieze]

This is the first time I'm hearing about printed keys on 31E, as it was a low cost entry model HP may have tried printed keys but they kept using molded keys on the other models for a long time.
For example, here is a picture showing an HP 48 molded keys where you can see the different colored plastics: http://users.ju.edu/hduong/repair/keyboard_back.jpg