[Model "A" Fords]

It isn't manditory to double clutch to change gears it's just one way to get the job done. The only object is to make the transition to and from gears smooth and quiet because grinding meens things are wearing.
I've always double clutch my model A's because that is what I was shown 50 years ago. When my roadster is cold I double clutch and touch the gas while in neatral for up or down shifting. After a few miniutes on the road it works ok without using the gas for up shifting but I still touch the gas while down shifting. My sedan, Moms Phaeton and my Brothers sedan all have their own little personalities that work for them.
Some people only single clutch by gaining the right timing and finesse that works for them and their car. The "A" can be power shifted (Not using the clutch at all) if you get enough practice but most people don't drive them enough to make it work and you can do alot of dammage while learning.
Once you figure out your cars personality it will be automatic which ever your method you use.
Happy driving!