Parallel DML vs DML order

Hi all,

Lets say I have these SQL Satements:

ALTER SESSION ENABLE PARALEL DML;

-- Create a new column for the sequence number.

ALTER TABLE a ADD (seqno NUMBER(38) NULL);

 -- Everyone gets a unique sequence number!

CREATE SEQUENCE seq_counter START WITH 1;

 UPDATE a SET seqno = seq_counter.NEXTVAL;

 -- Save the sequence number to use next.

INSERTINTO mrn (id, last_no) VALUES ('a', seq_counter.NEXTVAL);

 DROP SEQUENCE seq_counter;

Assuming the UPDATE is executed in parallel for table a, is it possible that the INSERT in table mrn does not always have the higher sequence number? Is it something documented by Oracle?