The one on the left is

ISBN 0-04-803002-3
First published by Unwin Paperbacks 1978

The one on the right is

ISBN 0-04-803002-3
Reprinted 1989

Trotter wrote:

The one on the left is

ISBN 0-04-803002-3
First published by Unwin Paperbacks 1978

That ISBN seems to belong to the 1978 hardcover edition?

The two I highlighted should both be reprints of the 1978 paperback edition, which is the 2nd from the left in the photo. Do these (3rd and 4th in the photo) not give an impression number? Cuz I’d like to record their cover change history