Of course there is a logical justification.
FortiGuard subscription always includes FortiCare, the hardware warranty prolongation. If a company puts HW under warranty, the overall lifetime counts. So, expired contracts are backdated.
Please note that backdating only occurs for 6 months. So, you never 'lose' more than 6 months.
Secondly, if you buy 2 or more years contract then FTNT will not backdate AT ALL. Your FTNT dealer should have told you this in advance.
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