Wall-paints SLIGHTLY wear and dull over time, but not much.

Your "New" touch-ups are just that, in a sense...NEW paint. As paint dries/cures, the sheen drops off as moisture leaves the curing film.
Will you notice a slight sheen difference for a month or so...Yes.
It mainly depends on how thick your touch-up film is...

A note on storing your paint:
* If you're still using the Gallon/Qt. container...Stop!
Pour off into something small that seals WELL!
* I always recommend small Pint or 1/2-pint GLASS CANNING jars. Obviously, NO AIR gets into these, therefore is ideal for storage.
>>> The less air-space the better! Add marbles or ping-pong balls to take up space.

Faron

I've had this happen if I didn't use the same type of roller for the touch up, and especially if I use a brush to touch up over rolled paint.

Faron- do you use a vacumn sealer on those canning jars?

I may try doing that with left over paint. My problem is some of the paint cans start to rust around the rim and then rust gets into the paint when you open the jars. I've also had some that the lining starts to peal.

Macy-
Yes...the rust problem is exactly why I recommend canning jars!
No----to the vacuum sealer!
Minimizing air-space is key, and easier!

Faron