VA Mahlers -- sound of original tweeter vs newer tweeter

Does anyone know what the sonic differences are between the original Vienna Acoustics Mahler and the revised Mahler that uses a different Tweeter . ..  after VA became unable to source the original tweeter?

Is the treble more prominent, more extended, more mellow, richer, thinner, etc?

Also, does anyone know at what serial number the new tweeters started?

Thanks for any thoughts!