大方廣佛華嚴經隨疏演義鈔 38.43

38.43

疏「今云不退有進趣義」者，不退有二：一已得不退，即前心定不動；二未得不退，即今此位念念進入，則是不退。

Regarding the commentary's: "Now, speaking of non-retrogression has the meaning of making progress," non-retrogression has two meanings: first, having already attained non-retrogression, which is the previous mind being concentrated and unmoving; second, not yet having attained non-retrogression, which means that in this present stage, advancing from thought-moment to thought-moment constitutes non-retrogression.