Well, given that copper sheathing had been about since the 1760s, you’d certainly expect the literal sense to have been current ever since then.
Er, yes, you would. The 1781 citation predates the OED’s 1795. There may well be earlier still.
The surprise really is that the figurative sense hasn’t been sighted any earlier than 1814.
Not really. The figurative sense of a word or phrase usually, though not invariably, follows the literal sense and not necessarily soon after. My post was intended to merely provide more information, not to take the gloss off your post, so I’m sorry it provoked a defensive reaction ("Well, given ... certainly ...).