53,s & 55,s have a few rare varietys of shoulder folds - no shoulders also a near - far that are rare . can't remember exact some of the 20,s as well,
Small Cents the key dates are 1922,1923,1925, and 1955 no shoulder fold. Large Cents 1858 and 1907H plus a multitude of valuable die varieties. Not to mention the unobtainable 1936 Dot variety which was minted in 1937 as a stopgap measure by the RCM.
Almost have my 2nd full set on Canadian small cents. There are some of the magnetic/non magnetic varieties towards the end there also that are semi-key.
Canadian cents are fun to collect. I've found a number of the key dates in foreign boxes such as a F12 1922 and a XF 1925 with a lamination error.