It is possible to combine datasets from multiple capture dates but it is highly discouraged as the quality of deliverables is generally dependent on many factors during a mission.
Repeatability of the flight mission parameters
The first thing to consider is the similarity of flight and environmental conditions between datasets of different dates. Sufficient image overlaps and flight parameters should be exactly the same. If you are using the same equipment, then you just need to make sure that the settings are the same across all the capture dates.
Remember that the accuracy of PPK-processed datasets depends heavily on the signal strength and quality received from satellite constellations available during the time of flight.
If your site is located in an area with erratic atmospheric conditions, this may result in inconsistent signal strength across the captures. Therefore giving inconsistent results from photogrammetry processing.
For more information on this topic or for flight recommendations, please see Flight Recommendations And Captures To Remove/ Filter Prior To Uploading For Better Reconstruction. You may also email us at email@example.com.