All TIE Advanced's are TIE Advanced, even if one advanced happens to be an X1.

It'd be like if they did a new Firespray-31 and it was called the Firespray-31 (Deluxe), it could still take either Firespray title.

"Stand back! I'm going to try science!!!"*

Darth Vader's TIE Advance X1 belongs to the larger set of ships called TIE Advanced. Thus it can take the X1 title, because it is a TIE Advanced.

P = TIE Advanced

S = TIE Advanced X1 (i.e. Vader's TIE Advanced)

All S are P.

Not all P are S.

Therefore, Darth Vader can take the X1 title.

(People with better mathematic skills, please correct me if I am wrong.)

*Quote from xkcd.

Close, but the circle marked S should be entirely within P.

Or to paraphrase, the X/1 title can be taken on all rectangles. Darth Vader flies a square.

It's to show that Vader is flying exactly one TIE Advanced only

Vader, Darth 1 each.

The X1 on Vaders pilot card is purely a little bit of fluff. His was the first.

And then star wars rebels happened.

The X1 on Vaders pilot card is purely a little bit of fluff. His was the first.

And then star wars rebels happened.

ouch

The X1 on Vaders pilot card is purely a little bit of fluff. His was the first.

And then star wars rebels happened.

Except much like the prequels before only a very small number of fans will remember it in a decade, while the OT remain beloved.