398 days is a year and 33 days, a little over a month. Is there a particular reason for choosing 398 as the limit, versus rounding down to 365 or 366 (a year), 395 or 396 (a year and a month) or rounding up to 400?
Apparently it’s a “renewal grace period” - not sure why that’s 32/33 days though.
Maybe 2 days to account for weekends/holidays, then 30 days to allow a cert nenewal PR to wend its way through the corporate bureacracy.
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One year is ⌈365.24⌉ = 366 days. One month is ⌈31 days + 1 leap second⌉ = 32 days.
At least for ISO dates, the leap second is included in the preceding day (i.e. it’s extended by one second)