I agree with Chris. It's quite common to find a mixture of zips on an original jacket. The RAF sheepskin flying jacket had either Dot or Lightning (Kynoch) zips. The Dots came with one pivot and a stamped slider or two pivots with a cast slider. Early examples have no AM and King's crown but have serrations on the back of the puller and are in nickel. Later ones have a flat brass puller and are so marked. Lightning zips are in two patterns (one that looks like an early Talon because of the association between those two companies) and the later characteristic pattern, which sometimes appears in nickel. Again, as with the Dot, early examples lack the AM markings.
I did one own a very early example (a civilian suit from the first year of production) that had Aero zips that looked original, but this is very rare. Any other zips are probably replacements.