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JFS license model is in general just the same as the license model used by Atlassian for all their products. As for the clause 7 you may find the same statement here: https://www.atlassian.com/licensing/purchase-licensing#softwaremaintenance-3
Example: Letlet's suppose today is 01/Jan/16 and your existing support & maintenance period expired on 30/Jun/15. Then upon purchasing a 1-year renewal the resulting expiry date will be 30/Jun/16 (30/Jun/15 + 1 year).