To firm the date up, the trays were first introduced in 1955.
Now, I might have dug myself a big hole, because if the transfers were affixed to the top and bottom, this would mean having two versions of the same transfer (one a mirror-image of the other), unless they were able to slide the transfers off the sheet and use them upside-down (if you see what I mean). I feel this would be unlikely.
So it is possible that the same transfer was used on all trays and was always affixed to the top surface of the tray. Not in a position to check with all the trays I have featuring this design.
Impossible to date precisely as this pattern was used for many years, but I think yours are sprayed enamel, not flashed opal, and would therefore be a later production model.