Hi Crystal,
There are a few more options :)
Create a Credential: Keep the username always the same - doesn't matter what. Store the number as password.
Each time get the number with Get Credentials, and then after updating it (incrementing it by 1) you store it again.
You'll get something like this in your calculation stage: ToNumber("""" & [Password]) + 1
Create a queue to track the runs: It takes the item, reads from preferably the item key the current Period ID. Stores it, And already add a new item ID incremented by 1 to the queue for the next run.
(Then you can either close the current queue item - not the new one you just added - but since a queue is great for reporting you can keep it locked until the robot is nearly finished and update it with the final robot result: Completed or Exception)
You can store it in a Database (Usually, Robots are not meant to run (only) local, and storing this value in a local file might give some trouble) Once you have the database, you can read it out, increment, store it. The system admin who helps setting up the BluePrism SQL database, can easily also create a small database for your robot.
Those options are with my current experience with BluePrism 4 & 5 - Maybe in BluePrism 6 you have even other options that I am not aware of.
Good luck!