SX 1846 - date type A

46 - higher than the 18

SX 1846 - date type B

46 - base alignment with the 18

This example 8 & 4 double struck

SX 1846 - date type C

46 just above base alignment

46 closer to the 8

SX 1846 - date type D

The 4 is higher - out of alignment

The 6 is rotated slightly backwards