The changes during the sequence updates are double protected: by an exclusive lock of the sequence block and by the SEQ latch. It’s not possible for two sessions to update simultaneously not only the same sequence but any two sequences in the same database.

If you would update a sequence inside a transaction and the AI logging is enabled for a database then you could restore the database to the state after any transaction and you could read the last sequence value. I don’t believe you will see the duplicate values for two transactions.

BTW, what is your OpenEdge version? There were a few changes in the ways how Progress works with the sequences. The most recent one was in 12.2