If you use the full field length of 18 digits and internal number assignment and have set the number range buffer to 1 (not loose to much unused number in case the server goes down) then it takes 31 million 709 thousand and 792 years for 10000 employees to use all numbers if they work without any break around the clock and enter 1 material master per second.
If you allow external number assignment then you can even make use of the alphabet, which means 36 numbers and characters to assemble a 18 digit number. If the Internet is not mistaken then this is called Septilliarde. (if these were all goats to be counted before sleep then I am sure sleeping beauty would woke up earlier than you 
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