Training, in this case, covers the possibility of the detector system not being a perfect indicator of whether the fire's been quenched or not. There may not be a procedure, but gathering information is not prohibited. Why not see what say the loops post discharge?
The delay between bottle discharge is due to the slow reaction of the loops. They are gas-filled metal tubes connected to (sometimes overly sensitive) pressure sensors and the system can take a few moments to recompose after being torched by burning kerosene or engine oil.