Lettering on Charles II Halfcrown

[arthurcrown 1]

There's this rather odd piece of extra metal in the legend above the word 'MAG' on my 1676 Halfcrown. Could anyone explain how it might of ended up like this pls ?

At first I thought it may of previously been an ex-mount but after inspecting the rest of the coin there's no signs of that anywhere. I'm Stumped

[copper123 1,521]

die break

[arthurcrown 1]

Thanks for that. Would they of usually fixed the die when this happened or just carry on using it ?

[Rob 3,154]

Carry on using it until it either disintegrated or became obsolete.