Can I generate a Functional Health report with blood tests from 2 or more dates?

I believe there are 2 possible ways to answer this question!

Can I enter biomarker results that were collected on different days?

You should ideally use biomarker results that were collected on the same day. There may be scenarios where this rule can be massaged:
Let's say you ran a CBC on one date and when reviewing the results realized that you should run an iron panel because of possible iron deficiency anemia. Your patient gets a chemistry screen run 5 days after the CBC then there is reason to put those results into one FHR.

Can I run a comparative report using 2 test dates that are not sequential?

The short answer is no. The comparative report is designed to run the result of the previous lab test by date next to the current lab test.

The historical report will provide you with a view of biomarkers collected over time.