This is Old 𝗨𝗦 Highway 91, not Old Utah State Route 91, so of course the number "91" won't appear inside a beehive shape. On the contrary, it also does not appear in a brown rectangle like Historic Route 66 does. I actually made a fork of AmericanaMap.org that colors "𝚄𝚂:𝚄𝚂:𝙾𝚕𝚍" Highways as green (consistency with sign blades). Again, "Old Highway 91" could refer to any old highway, so keeping that in 𝚗𝚊𝚖𝚎=* while not at least giving it 𝘴𝘰𝘮𝘦 𝚛𝚎𝚏 tag could lead to ambiguity.