XEP-Remarks/XEP-0203: Delayed Delivery
There are multiple hops involved in delivery of a stanza, multiple points where it may be delayed. It may even be delayed multiple times, e.g. because the users client had to resume their XEP-0198 session and their server took its sweet time to get s2s up and running.
Thus it makes sense to allow multiple delayed delivery payloads on a stanza.
Missing from attribute
A stanza sent without a
from attribute implies
from=senders full JID. Applying the same to delayed delivery makes sense, ie missing
from means that it was the original sender that had a delay.
Including ones own full JID would also be a privacy leak in the context of (semi-)anonymous MUC.