The importer caches the files url including any query params, for example if the importer came across the following image:
https://image1.png?ver=1
it would download it if it had not previously and then if it was to import the same image again it would link to the existing image in your wordpress media library (instead of downloading the same image twice).
But if it found the image with a changed url such as:
https://image1.png?ver=2
it would download the new version of that image storing it against the url.
James
I think what you are saying is correct, if you do notice its not working how you would like then i can help you to resolve any issues.
James