The answer to this question lies in the definitions found in FAR part 2. We start with the definition of micro-purchase, which is "Micro-purchase means an acquisition of supplies or services using simplified acquisition procedures, the aggregate amount of which does not exceed the micro-purchase threshold." The last part of the definition for acquisition is "Acquisition begins at the point when agency needs are established and includes the description of requirements to satisfy agency needs, solicitation and selection of sources, award of contracts, contract financing, contract performance, contract administration, and those technical and management functions directly related to the process of fulfilling agency needs by contract."

So the micro-purchase threshold applies to each acquisition that will have defined requirements to meet agency needs. Cognizant government officials decide which requirements will be included in each acquisition. The aggregate amount of each acquisition must include all delivery periods and options IAW FAR convention 1.108(c).