Lustre is the shiny like new appearance that all new coins have when new and un touched. Coin collectors and dealers can easily tell the difference between a coin posessing original lustre and an aftificial polished coin. As you know, once the original lustre has faded, it can never be brought back. That 1963 Threepence has about full original lustre, and original lustre always tends to look about that kind of colour on threepences of EII. Although on some early George VI coins it often a different hue. It's difficult to show you in a scan, but over time if you get a few full original lustre threepences from reputable dealers (like me for example ;-)) then you'll soon learn what they should look like. As they are normally not expensive and normally not that widely collected (compared to other types), I would think it unlikely that your threepences have been polished. Post pics of them, and we'll see.