Good points, Stuart. But one thing that strikes me is that even if you limit your penny collection to Freeman types only, and nothing else, I'd say it's still virtually impossible to obtain every single last specimen type, even over a 60 year collecting period. Some, such as the Freeman 2,5,19, 34,44 and every single proof type, will elude you for a lifetime. OK, you might get one or two of the examples I mentioned, but not all. Plus, that's just a sample of the "almost impossible to get your hands on" brigade. There are innumerable others, such as die No 5 under 1863 date.
Even then, you're almost certainly going to have to content yourself with a fine or less example of the rarer Freeman varieties, you do manage to obtain.
Tough old business being a completionist