convert external sources: How does it know which ones to convert?

Question

I'm experimenting with the WwiseConsole convert-external-sources command, using the --source-file parameter. I noticed that it doesn't convert all of the .wav files in the .wsources file, and this is because of the wwise.dat file that also gets generated. If I delete the wwise.dat files located in a platform/lang folder, that folder will get completely regenerated. So far so good, but what I'm confused about is: If I run convert-external-sources twice consecutively, it still re-writes the same 18 .wem files. Why is it doing that? Shouldn't it leave them alone, because they already exist? If I delete

Follow up question: If I'm running this on a build-machine, and I want it to rewrite certain existing .wem files (say, for .wav files that have been modified) but not others, is it up to me to generate the .wsources file in a way so that it only contains .wav files that I want to convert or re-convert? Should my process also delete existing .wem files that need to be re-written just to make sure that the WwiseConsole writes to them?