Winding bobbins

I was just filling bobbins to start on the quick rose sketch I posted here. ( I know I should be finished by now) There was some thicker cotton wrapped around the old bit of paper in the foreground of the image below. The thicker thread is wound onto the bobbin and the image is stitched upside down. When I wound off the cotton I found the paper was an old envelope ( I can't make out a date)  with a King George V1 stamp on it so I am guessing the thread has been on that envelope from approx 1952 or earlier. Thanks Nancy for the bag of threads. So now I am thinking I need to keep all the bobbins etc that I empty of thread.

Bag of threads given to me for this project

Envelope has to be pre 1952 as the stamp is King Gorge V1 (14 December 1895 – 6 February 1952) I have covered the name and address as I don't know the recipient and they or family  could possibly still be at the address.