On the Copyright page of most books the numbers 1 - 10 are often printed sometimes in descending sequence. Wh?

Answer 1

Those are the numbers of the print run. On the second print run they will have the numbers 10 down to 2, on the third 10 down to 3.

If the book has had more than ten print runs, the numbers will go from 20 down to 11 (or so), and so on.

My Bantam books Catcher in the Rye says Bantam edition 1964, 62 printings through April 1986, and then the numbers are
71 70 69 68. So it's from the 68th print run. I bought it around 1990.

Answer 2

it tells you the number of times it has been printed. :)