"The ordering-prefix may also be used in Modification requests to
specify which values to delete, and in which position values should
be added. When processing deletions and insertions, all of the
ordinals are recounted after each individual modification."
I think this is unworkable in any situation where multiple clients
perform operations - clearly there will be race conditions. The only
way to avoid those race conditions in the delete case is to include
the value, which makes the ordering element moot. I don't believe
there is a reasonable method of avoiding race conditions for inserts
in the current scheme. Perhaps adding a control with the values
either side of the insert point would help, at least by notifying
the time T2 modifier that things have changed.