Opening the black box
The most valuable part of the specification review is quizzing the developers on the extra work they had to do. Which special cases did they have to write additional code for? Explicitly ask that question because it may not be evident from either the product owner requests or your exploratory testing what work has been necessary.
You can invite the developers to present the architecture to discuss how the different sections work together and how this feature was implemented. This loses the naivety that was helpful during exploratory testing but, at this stage, it’s much more important to be an expert in the workings of the feature.
Understanding the architecture helps explain which variables are independent of each other and can be tested individually and which you should expand out to test the entire matrix of possibilities. It also helps show areas of the test plan that need to be covered in detail and which can be checked with a single test. This...