Dates and session numbers are important ways of identifying documents. For the main organs, the first session of the United Nations was in 1945. To determine session numbers, subtract 45 from the year in question. For example, for the year 2000, subtract 45, to find that in the year 2000 the UN is in its 55th session. Note that sessions begin in September. Unfortunately, subsidiary bodies function differently. Their sessions can be numbered according to when they meet, not the session of the United Nations. Thus a subsidiary organization in 2000 could be in its 30th session, or even in its 60th session (if it meets more than once a year).
Note that some document symbols include the year of the document or the session numbers, but others do not. This is due to the different reporting procedures of the different organs and subsidiary bodies. For example, the Economic and Social Council uses the year in their document numbers (ex: E/2000/106), while the General Assembly uses the session in their document numbers (ex: A/RES/53/202). It is also due to historical changes in each body's reporting system. For example, the General Assembly began by numbering their documents sequentially, without regard to year. Only in 1976 did they start to number the sequence fresh each session and include the session number in the document number. The Economic and Social Council made a similar change in 1978, and the Security Council followed suit in 1994. Subsidiary organizations work in their own ways.
Document dates can also be confusing. A document might have several different dates. For instance, the date under the symbol on the document itself is the date of registration of the document. This is the date most commonly used when identifying the document. The date at the bottom of the document, usually near the barcode, is the date the document finished processing. Third, the documents have an issuance date, which can be found by looking at the daily list of documents. Fortunately, exact dates are not required for Bluebook citation.