I don't know if this is what you are referring to but their are three variations of the SW99 series. The most common is the SW99, which is the AS (anti-stress, similar to TDA). The SW99 QA has a small decocker button that is only used for take down of the pistol. Otherwise it only has the DAO trigger, like a Glock. Then the third variation is the SW990 and SW990L. This does not have a decocking button at all and has the Glock like trigger of the SW99 QA.
All of that being said the straight SW99 is the most common and regulary seen version of the series. Any one of these you run into will be a great pistol.