It should be possible to call swh-identify like this:

$ swh-identify foo.c bar.c Makefile
swh:1:cnt:524175c2bad0b35b975f79284c2f5a6d5eaf2eb4    foo.c
swh:1:cnt:524175c2bad0b35b975f79284c2f5a6d5eaf2eb5    bar.c
swh:1:cnt:524175c2bad0b35b975f79284c2f5a6d5eaf2eb6    Makefile

whereas currently only a single argument is supported.

The relationship between the --type option and this feature request is non trivial though. The best choice is probably to mandate --type auto when multiple arguments are given.