As mentioned, it depends on your definition.
I make custom bowstrings--choice of materials, colors, strand count, serving type, serving size, loop size,endless, flemish, etc. etc. etc.
I've made a lot of the same strings for different people. Every one may not be unique or one-of-a-kind, but they are all custom made to order.
I do get what you are saying--a more accurate term would be "production bows with options"--but we've come to accept that as "custom" when it comes to bows.
Chad