Since we had cog boards in the shop "back when" building a custom FW or just replacing a single worn cog was easy and cost effective for 5-7 cog designs as the tech changed.
Still have custom 14-18 5 cog, 13-23 6 cog and 12-20 7 cog, although none are still in service they got the job done back when.

edit: That being said the Shimano cassette design at 7 cog and up w/ a stronger axle and the ability to swap gearing w/o a bench vise was a permanent game changer, no nostalgia here for the FW.
Too bad a Cog Board isn't available for 10-11 cog designs today to replace that worn 16T......

-Bandera