The 95/100 gear ratio is the same as a 19/20 ratio (divide both numbers by 5 to see this). So the 95/100 gearing lets you convert the 20TPI setting on the machine to actually cut 19TPI.
Other thread settings that can work abound mathematically but perhaps not physically. For instance, to cut 19TPI using the 23TPI setting you would want gears with a 19/23 tooth ratio, or 38/46 (double the tooth count), or 57/69 (triple the tooth count), or 76/92, or ... you get the picture.
Any thread selection on the machine can be mathematically converted with the right gears to cut 19TPI, but those gears may not be physically realizable.