The GLAD UMD dataset on the TCC can be found here. The TCC and Loss datasets are prepared by GLAD UMD utilizing different input datasets and algorithm. So the forest disturbance can be calculated from both datasets. We will be calculating the first disturbance by combining them.

The first disturbances are the first year in the time series for which the TCC drop to zero (or your country threshold) and the last disturbances signifies the last year of change.

With the help of the Earth Engine, we will try to generate the first and last disturbances information. The logic is presented as pseudocode below.

for (i=1; i0 or (tcc[i][y][x]==0 and tcc[i-1][y][x]>=10))){

The source code for calculating disturbances is here.