a simple method would be to have a hidden date field associated with the default document type in the list and to set that at a specific date e.g. 25th December 1970 for example. It could then be easily used as the identifier when you want to remove the list.
If you want to have a hidden field like this added to the type, you'll need to set the 'Allow Management of Content Types' to 'Yes' and then you can either add a new column to that and set it as hidden by default or create a new column and again set it to hidden. Importantly it wouldn't be visible in any way to end users etc. but would be useful programmatically.
Hope this is a useful alternative. Alan C.