Swap files and swap partitions are different. calamares will both happily use both (my systems often have both, swap partition being shared by my dual-boot systems), but certain options of install will cause existing swap partitions to be erased.
Many of my observations with swap files can be found here on a link I’d already posted.
We do QA-test installs that re-use swap partitions, though much of the QA checklist involves full disk installs that erase everything thus only the default 512MB swap file will exist post-install.
In my experience the installer will do whatever you instruct it, but yeah it’s silent in some options and could give more detail (in those cases it will re-use swap file where not formatted, or create swap file (512MB) if format). It’s the silence on some options that caused me to create the aforementioned wiki link (where you might note I use language used in our QA-checklist).