If you used the current only quarterly set, then it does start in 1992 and you need to use a set of back data. WRDS support has a section titledOverview of Compustat that explains how COMPQTR holds the complete data.
For example, COMPQTR Combined Industrial Quarterly not INQ P-S-T Industrial Quarterly.
In general, the quarterly data add up if you take care of fiscal year versus the calendar year for selecting the 4 quarters. Some differences come from restatements to the quarterly data. The note below helps to explain this issue.
In most cases, the Annual Compustat items are as first reported. If a company restates or makes a correction for prior reported data in its 10K filing, then extra data items such as DATA117-- Sales (Restated) hold the revised figures. DATA12-- Sales (Net) (MM$) would not change (under most circumstances).
Compustat does standardize some items, such that they are not always exactly as reported, but this is usually a case of a data correction, not a company restatement.
For quarterly data, the story is different as the standard Compustat Quarterly set does not have two types of items—original report and restated. If a quarterly data restatement occurs, the originally quarterly values are removed and replaced with the restated values.
Compustat’s Unrestated Quarterly set is more analogous to the standard Annual data items and is closer to what was available to what financial markets could observe in real time. (Compustat is also developing a ‘Point in Time’ data service that is, even more, representative of the real-time data.)