The standard does not need that documents including records need to be numbered.The requirements are
1. Clause 4.2.3 e) to ensure that documents remain legible and readily identifiable
2.Clause 4.2.4 A
documented procedure shall be established to define the controls needed for the identification
How you ensure identification or establish a system for identification is upto you.Auditor need to verify effective implementation of the system.If the auditor finds that the determined system is not appropriate for the organisation,he need to explain to auditee why it is not appropriate.
Identification of documents through numbering system is now practised for quite a long period and may be it started from ISO 9001:1987 or even earlier.It would be interesting to find the inventor of system.Even though there is a number on the document,the name of the document is also mentioned.So you will find "List of approved supplier PO-VEN-01" or "Procedure for recruitment HR/PR/05".In this way we are ensuring double identification.Rarely we find documents with only number.
Here,I would be interested to know whether the "planning" you mentioned is in your brain or the information related to planning is captured in some media.The definition of document is "information and it's supporting media".So if the planning is in your thought,it may not be considered as document.So no need of identification even.