A supplementary expert report may change the question you must answer

The expert file has grown since the first response

You prepared a response to an adverse report, then a supplementary report arrives. Read it with the lawyer and appropriate technical adviser. Do not assume it merely repeats the original or replaces every part of it. Identify what changed and what remains. An earlier summary may no longer describe the issue the parties or court are being asked to consider.

Keep the report sequence clear

Retain each report with its date, author and relevant covering correspondence. Record whether the later document refers to new information, testing, instructions or a changed opinion. Avoid overwriting the first report with the newer file. The history can be important to understanding why a conclusion was modified and which assumptions supported each version.

Recognise the role of an updated opinion

The NSW Land and Environment Court's guidance addresses supplementary reports when an expert materially changes an opinion. Ask the lawyer which rules apply to the actual proceeding and what response is needed. A change does not automatically prove unreliability or settle the dispute. The substance and explanation need assessment rather than an argument based only on the fact that a later report exists.

Source: NSW Land and Environment Court: Expert witness code of conduct and duties

Use a hypothetical technical change

Imagine the original report assuming a particular product was installed, while later records establish a different product and the expert issues a supplement. Your response should address the revised factual basis. The example does not determine whether the new conclusion is correct; it shows why continuing to rebut only the earlier assumption may miss the current issue.

Check the effect on your own material

Ask your adviser whether a factual schedule, technical response or proposed questions need updating. Keep any earlier response identifiable rather than silently rewriting it. Do not coach an expert to maintain a favourable opinion despite information that requires reconsideration. Professional assessment should address the evidence honestly, including changes that do not support your preferred position.

Track the current issue and next step

Record the substantive change, supporting information and the response required under the actual directions. Monitor relevant dates with the lawyer. A supplementary report deserves a focused comparison, not automatic acceptance or dismissal. The useful outcome is a clear understanding of the opinion now expressed and the evidence needed to assess it, while preserving how the issue developed.