First of all, I cannot believe that you have had this model all these years in showroom condition!! Did you ever "play" with it? Or was it a case of take it out of its box, look at it carefully with a great deal of childhood love, and then carefully return it to its box?? I find it quite unbelievable and at the same time, very refreshing!
Jacques, as for "stereo", I think Meccano used this terminology, not in relation to rubber stamping, but in the context of "two", one on either side of the model. At about this time, stereo sound in amplification was becoming the "in" thing, although the technology dates back to the 1930s, it was not until the mid 1950s when the system became commercially viable in recording production. To achieve "stereo" sound in a home system' two or more independent audio channels were used with a modified stylus, together with two or more speakers. So I think the draughtsmen in Meccano used the terminology to describe two when the operation is repeated on the other side. What does the drawing actually state?
I have just checked my drawings for the 965 and it is interesting to see the note state:
"EUCLID TRANSFER RIGHT HAND STEREO AND NOTES ADDED 3.1.55"
No mention is made of LEFT HAND STEREO. As the drawing shows the left side of the truck which seems to indicate that the use of the word "stereo" is intended to mean the Euclid transfer is the same on the other side.