why do mint figures change over the years

[Basil]

gee didn't the 30's penny jump from the 70's to the 80's, thanks serial.

Probaly stating the obvious but the value of the key dates really exploded in the early 60's when the change to Decimal currency was announced,i think the Catalogue values took a while to catch up but the 1930 Penny did rapidly rise in value after the early 1970's slump.

Scans from the other Thread....Renniks 4th edition 1966.I have some interesting Newspaper articles from the same period i will post them when i get home later in the year.