they are sold at random. I think all of them have been made. if so then all they do is pick a pair at random at the warehouse and sell it to you or ship to the store. if they are all produced and sitting on warehouse shelves at the same time you have equally the same chance of getting number 2 or number 200.
ps. I think the #130 you have is not the serial number but the length measurement of the arm.
ps. I think the #130 you have is not the serial number but the length measurement of the arm.