Because a document with details of STC's work is not complete. Lack of procedural details of the connection pipes, HDPE, and various methods according to the OE ever requested.
The document contains details of the STC's work is not complete. Lack of details of HDPE pipe welding process and the various methods by which the OE had requested.
Because the document of the STC details of working is not complete. The lack of details of HDPE pipe welding procedures and methods according to the OE was requested.