What is indexing against a recorded certificate?

Indexing against a recorded certificate refers to the process of associating additional patent numbers or application numbers with a document that has already been recorded in the USPTO’s Assignment Division. However, the USPTO does not process such requests for ‘indexing’ or ‘cross-referencing’ unless a new submission is made.

According to MPEP 315, The Office does not process requests for ‘indexing’ or ‘cross-referencing’ additional patent numbers or application numbers against a document, other than an assignment, previously recorded in the Assignment Division.