The 1923 Australian Halfpenny are relatively rare because there were only 15,000 minted.
There were only ever 7 or 8 British 1933 Pennies minted.
As a word of caution, there are many reproduction or copy coins available.
For reasons known only to the Royal Mint, there were only 120,000 minted.
British George VI Pennies were usually minted in the tens of millions.
They are not rare at all.
Not a rare date. No added value in circulated condition.
British, U.S. or Canadian? Post new question.
Nothing in that range is classified as rare, but any British Penny in mint condition from those years would have a modest collector value to it.
No, the 1951 Lincoln cent is not rare.
There are no rare 1912 British Pennies. The "H" on the reverse, below Britannia and to the left of the year, indicates that it was minted at Heaton in Birmingham. There were 16.8 million minted.
About 3 cents if it's an American cent; 1951 British pennies can be worth considerably more. Please see the questions "What is the value of a 1951 US cent?" and "... 1951 British penny?" for more details.
Glynis Penny was born in 1951.
Penny Werthner was born in 1951.
1933 one penny, 1952 half crown, 1936 Edward VIII brass three pence...
Not much, only about 50 US cents or so. It is a rather common coin and not rare.
The Royal Mint did not mint any One Penny coins from 1955 to 1960 inclusive.