Is it possible for PubSub to lose messages without subscriber knowing?

[AqlaSolutions]

Assume there is sequence of events - 1, 2, 3 - which should be received by a subscriber. When the subscriber becomes temporarily unreachable but not long enough to be blocked from the cluster, is it possible for him to lose 2 and receive only 1, 3? Does it have any way to know about the lost event? Also, is it possible for him to receive the events out of order: 1, 3, 2?