Information Needed - 5/1968 British 10 Man Compo

[Amelieee1]

Hi all, I recently acquired this British 10 Man Composite ration pack from 5/1968.

Its the earliest compo I've ever seen apart from pictures of WW2 ones. - Closest I have seen to this is 1974, and a menu sheet from 1969. Nothing actual can wise before 1974.

Anyway, what I came here to ask about is, does anyone know what menu X could mean? This came with no menu sheet or sundries. 22 cans of food but none of the tea/coffee/chocolate etc.
My theories and some others theories for the menu X are:
X = Experimental (Testing out new mains/meals? - This lines up with there being lots of desserts/etc/mixed mains)
X = XYZ / Example (Training aid/example?)
X = Extreme Enviroments (Hot/cold? - would support the amount of desserts to increase calorie intake?)

Any ideas/info would be appreciated greatly, as currently I dont know much about this thing, and it being the earliest one I have ever seen, it just makes it that bit harder to get information.

Here are the pictures from the listing, havent had time to take my own yet: