What does the first character represent, if anything?
The best numbering system is non-intelligent, sequential numbers. The length is up to you. The use of dash numbers is no problem, just define when you use dash numbers.
I have been at a company that used a unigue number for most parts. If the part was used in a weldment, then the weldment details would be given dash numbers of the unique weldment number. Dash numbered parts were never sold as spares.
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