For @Citizen H, Yes, it looks like there are problems with a number of the letters on the 1776 twopence, but that is not scarce for that era. Interesting, but not changing the value enormously.
For @DaveG38- Does your 20 missing include 1 and 2 pence coins? I left those out - they are so small they drive me up the wall! I only went for the 3 and 4 pence coins - missing both the 1765s, which are always very scarce, the 1792 3 pence (wire money), and then for some reason 1743 and 1703 4 pence. I haven't searched for these for years, maybe I should have another look.
For @Mr T, I agree on patience. I got the majority of my collection through serendipity rather than great expense. Many came to me when I was dealing as part of bundles offered to me for sale in the markets, or in response to general newspaper adverts. These days too many people are internet savvy and so these bargains don't happen much anymore. Recently I have had to lay out more serious money to fill the remaining gaps!