87th Grenadier Coy jacket button
 

On the epaulets an unknown button, normal Nutting buttons otherwise throughout, are the initials the coat manufacturer ?

This will be simply one put on to replace a missing one at some point during the jackets life. Probably by some well meaning curator or an owner to prevent it flapping around when on display.

Coats of this date were issued annually to soldiers via large contracts and were effectively worn out and discarded at the end of a year when the next round of uniforms were supplied.
They were not govt property, but regimental property (though thecost was reclaimed fromthe Crown) and were marked with the number of the soldier wearing them, who subsequently became responsible for it's damage or loss.

buttons
 

Thank you for your useful comments, the both epaulets have the same buttons and the button thread looks identical throughout the jacket.

The letters are A.I.D.
Are the other buttons identical?

All 87th Regimental...except both epaulet