Although December 2019 may ‘officially’ be at the start of Cycle 25, we have been and are still seeing a mixture of both Cycle 24 and 25 sunspots – there is usually an overlap of 18 month or 2 years between cycles. Sunspot from the two cycles can be distinguished by their latitude with old cycle spots being near to the equator and new cycle spots being at higher latitudes. The different cycle spots, in the same hemisphere, also have opposite magnetic field polarity.
The ‘official’ date of start of the new cycle is based on monthly sunspot numbers which are smoothed over a period of 13 months and so the minimum value is not known for 6 months or so. It is possible this date may get revised if the coming months have very low activity – activity in September was very low with almost no sunspots.