I emailed Muntons and asked them to explain the numbers on the can in relation to the date the product was manufactured. I got the following response. I give high points to Munton's customer service. Correspondence follows:
Subject: use by date?
I frequently use muntons malt extracts that are packaged in homebrew kits. I would like to ensure that I use only the freshest ingredients. Can you tell me if there is a date of manufacture or a "use by date" marked somewhere on your extract products (specifically your cans of malt extract)? The two cans that I purchased were numbered: 2171 XB24609 9023 and 3519 XB25105 9098. I'm in the country and dealing with a small shop that appears to have very little inventory turnover. Thank you for your help
Good morning Frank
Some kits have a date stamp on them, but the ones you refer to were canned on 23rd Jan 2009 and 8th April 2009.
The number after the XB number relates to the date it was canned by Muntons ie 9023 means that it was canned on the 23rd day of 2009 (23/01/09) and 9098 means that it was canned on the 98th day of 2009 (08/04/09).
Hope this helps.