Thanks for the comments folks.
Yes, experienced painters recommend painting a bikes topcoat all from the one can, if possible.
'Cause that 2nd can they supplied may not be exactly the same shade.
And I have seen this myself.
Mixing it up in a larger can then splitting into 2 smaller ones helps prevent this.

This, and other pics, should be good enough to get a match from.
Seems it was a single stage enamel pearl, in common with the numerous other shades of
polychromatic enamels Enfields used over the decades.
Curiously, HD also used a pearl type shade they called HiFi blue. You can still buy it over the parts counter. ?
A stronger shade of blue though, it would be a mistake to assume it was the same.