Heya..! Just got done watching Uncle Albert's second episode. "Hole In One".
This wiki states that "Gladstone" is never officially stated as his middle name, but in the court scene for this episode, his full name is stated, and Gladstone is his middle name in this episode. So ya see... it IS stated.. officially. Just thought you may wanna clear that up!
- Stevey The Ex-Eevee