When I first started to write technical reports, I made the mistake of writing Section 8, Discussion of Results, first. This was difficult because I tended to ramble. After writing that section, I would then try to arrive at and write the Conclusions and Recommendations sections. Wrong! Backwards!
Now, I first arrive at my conclusions and recommendations based on the raw data and then I write those two sections. Every conclusion must then be supported by the data. By knowing my goal (i.e. Conclusions), organizing and writing Section 8 is much easier. I think that the closer link between the conclusions and the results also assists the reader in understanding the report and in accepting the conclusions and agreeing to the recommendations.
Support all statements
The underlined sentence above, while directed at the report Conclusions, also applies to any statement in the report. When I am writing, I constantly ask myself...what data support that statement? Then I point the reader to the data in a table or plot that shows the supporting result. You shouldn't leave it to the reader to find the supporting results. If the reader isn't immediately pointed to the supporting data, then the statement is assumed to be unsupported. I have read reports that are full of unsupported statements. To me, they are just opinions. I don't know whether those opinions were formed before the study or because of the study results. Either way, I have a negative view of the report.
Technical studies often turn up unexpected results unrelated to the original study objectives. As principal investigator, you may or may not realize their importance or significance. You should therefore include them in the report.
Should you include the unexpected outcomes in the Conclusion section? I think that is your call. I would probably include them if I know that they could have a significant impact on the greater project for which the study was undertaken. If their importance is small or unknown, I would not include them in the Conclusions section because it might confuse or distract the reader from the main conclusions. Regardless of whether or not they are in the Conclusion section, they should be in the Results section, possibly in a subsection "Other Results".