The following information obtained from UNAVCO's online DOI system:
(https://www.unavco.org/data/doi/search/search.html)

Greenland GNSS Network - GMMA-Gamma O P.S.
Start: 19-Aug-2009
End: 31-Dec-2011
Bevis, Michael, 2009, Greenland GNSS Network - GMMA-Gamma O P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/T55Q4T4V

Greenland GNSS Network - GMMA-Gamma O P.S.
Start: 19-Aug-2009
End: 14-Nov-2022
SDFE, The Danish Agency, UNAVCO Community, Bevis, Michael, 2009, Greenland GNSS Network - GMMA-Gamma O P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/B78A-BZ29

Greenland GNSS Network - GMMA-Gamma O P.S.
Start: 01-Jan-2019
End: 14-Nov-2022
SDFE, The Danish Agency, 2009, Greenland GNSS Network - GMMA-Gamma O P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/56NY-2R07

Greenland GNSS Network - GMMA-Gamma O P.S.
Start: 01-Jan-2012
End: 31-Dec-2018
UNAVCO Community, 2009, Greenland GNSS Network - GMMA-Gamma O P.S., UNAVCO, GPS/GNSS Observations Dataset, 
https://doi.org/10.7283/MR24-XN85