Have data on a spreadsheet:
Shipdate Quantity

The data goes back 5 years, and is constantly updated with new
shipments being added.

Would like to have on another sheet a rolling summary of how many have
been shipped within the last 12 months, the previous 12 months to
that, etc, up to 5 years.
So the summary would look something like this:

Present to 12-Mos. 29
13-24 Mos. 55
25-36 Mos. 36
37-48 Mos. 55
49-60 Mos 39

TIA for any ideas on this.

Pierre