So, there's really two parts to this:
1) How do I use a token value across multiple document classes?
2) How do I remove (just) the first page of the batch (e.g., a batch cover sheet)?

For #1, you want the Token Collector and Token Retriever processes.  The Token Collector will store the assessment number token for other document classes to use, and the Token Retriever will be used in the document classes to get the value and store it in a field (or however you want to use it).

For #2, it's a little more complicated.  Set up the batch cover sheet as its own document class with its own identification condition and the Token Collector process.  However, actually deleting the document (you can remove its only page with Page Removal, but that doesn't delete the document itself) doesn't seem possible within Quick Fields itself.  One workaround is to have the document class invoke a trivial Workflow just after storage that deletes the entry.