M1 -64 question about Mitchel covers

[gaz232sqn]

Hi.

Here is an M1 -64 from my collection for you all to check out!

This lid is my fave model 64, as it's one month younger than i am,

1969 a fab year!!
Any way the question is....
The Mitchell cover is unusual (in my collection anyway) as its got the eyelets for the bales and straps to go through i think it's dated 68.(My other Mitchells just wrap around the bales instead.)
Does anyone know when the change took place with these covers?
Enjoy

Gaz