Only Bambulab themselves will be able to give a very precise answer, because they know where and when exactly the K value is used.
I found a reference in the Wiki a long time ago where the calibration is described. I was concerned about your question in exactly the same way.
In any case, I recommend that you check the K-value by carrying out a second calibration. Sometimes the automatically determined value is not correct. For example, I had a value of 0.011 for green PLA. I had it calibrated again and got a K-value of 0.022. I started the manual calibration and saw that a K-value of about 0.01 was correct. This is a problem if you calibrate automatically before each print! The printer could be working with an incorrect K-value. The reason does not matter at first.
After the K-values are found, they are stored. If you ever reset the printer to factory settings, the K-values are all gone.
And now the wiki comes into play. According to it, the stored K-values are used for printing. Since I could not read the opposite, all K values are also used as they are stored. Before printing, check the AMS settings to see if all filaments have been properly assigned and, if necessary, select the correct profile for the filament inserted in the AMS from the drop-down list at the bottom so that the K-value appears. If no K-value is noted in the AMS view, a default value is used for the filament in question, according to the wiki.
If you have a multicolour print and calibrate the K-value before printing, this only happens for one filament. The K-values for the other filaments are not determined before printing. To be able to work with the K-values, you have to determine and save them beforehand. This way, even when printing with several filaments, the correct K-value should be used for each filament.
Have a nice day!