A cone penetration test, called sondering in Dutch, records resistance as an instrumented probe enters the ground. The results help assess subsurface conditions. The test provides evidence for design; it is not itself a foundation design.
How this term relates to your project
The location, extent and interpretation of investigation should match the project question. For an extension, this includes information needed for the proposed structure and its relationship with the original building. Have the required additional evidence identified; nearby records do not replace that judgement automatically. Discuss access to the investigation location and any necessary preparation.
Retain the report with clear identification of where the test was performed. The structural designer should be able to trace decisions to the information used and recognise uncertainties that remained when the design was prepared. A graph without its location and context is not a complete basis for comparison.