They don't expire, they're coded for the CPU serial. With the latest bootcode/firmware, once the licence is correctly read for your system a OTP (one-time programmable) bit is set in the processor and the licence is permanently installed.
That extra email is probably a SNAFU by the RPF folks who run the licencing service.
Microprocessor, Raspberry Pi & Arduino Hacker
Mainframe database troubleshooter
Since 2012: 1B*5, 2B*2, B+, A+, Zero*2, 3B*3
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