Sisface23,
Thank you for your contribution. That is quite the clarinet you have found. I have never seen a Soprano Pedler Plateau, so you have a rare gem.
I would love to see photos, and know whether you moved forward on its restoration.
Sid signed late in the game. He may have even stayed behind at MBIC, for a time. To answer your question, Yes; in my estimation, the guarantee bond makes your valuable clarinet significantly more valuable. Can you tell me who the manager was at the time? (Was it RO Thompson?)
Even if it never plays magnificently (and it may well), you certainly got quite a fantastic deal, as you hold an historically significant relic.
Cheers-