One is the drop of visual acuity due to focussing error:
your 20/xx score without glasses or contacts.

The other is how well the visual/neural system can perforn when in optimum focus. This is for many people near 20/20, but some can do better, and some will never get 20/20 whatever optical correction is used, spectacle contact or laser, due to a limitation somewhere else in the system.
(think film photography: you can fiddle with your camera all you like, but if the processing lab is poor, you’re not going to get pin sharp pictures.)
Lasik, glasses and contacts all aim to throw the eye into "good focus". How good that is hangs on the clarity and smoothness of the cornea and crystallline lens, the grain of the macula and the neural processing.

Now, with lasik it’s extremely likely that your vision without glasses will improve. If the Rx result comes out very near zero, the *unaided* vision could be 20/20 or better, depending how well the rest of the eye works.

But for a good number people the best vision after lasik will be detectably worse than the best with *with* glasses before lasik, since the quality of the cornea will have been reduced.
(detectable, that is, by careful examination: not necessarily in the day-to-day experience of the patient)

For some this reduction in quality shows in flare and halos, especially at night, but more rarely it can even affect the best line that can be read on a high contrast letter chart.
(It’s often more obvious on a contrast censitivity chart, where the letter don’t get smaller but get greyer, paler, on each line.)

So, to return you your original question, if you’ve had better than 20/20 unaided or with glasses in the past, then better than 20/20 is a possible outcome with lasik. But it’s not assured.
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