Are journal's UB & UP entries guaranteed to be in 1-2 sequence?

Are an update record's UB (Update Before) & UP (Update After) entries
guaranteed (no quibble, rock-solid, cross-my-heart) to be in 1-2 sequence,
with NO possibility of another entry being written between them?  I could
not find any reference to this in the manuals, and so I must now presume
the possibility exists and must store the UB entries in an array, waiting
for the UP entry to arrive and match to the UB entry by JOCTRR (the RRN)? 
Since the program is RETURNed without setting LR on after each entry is
processed, the UB entries will still remain in the array on subsequent
calls to the program, correct?

I am writing an exit program to a RCVJRNE command.  I need to compare
before & after images on an update to a record to determine if I need to
take a specific action.  The files being journaled are getting both the
before & after images journaled.

Also, as I now see that the exit program is RETURNed without LR on after
*each* journal entry, doesn't that have the potential to be a resource
drain?

TIA, GA

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