Rudder

As a general rule, we should not save an inventory that is older than the date of the currently saved one.
It can happen when for example an old inventory is sent back after a relay restart, or when Things Happen.

An exception to that rule should be if the currently saved inventory for that node is in the future. In that case, the currently saved inventory is likely an error, and we shoud save the current one to avoid the case where a bad clock lead to an inventory in 2038 and nothing would ever been accepted again.