It does appear that they are doing some editing/arranging (but I'm not going to check at their prices). By this fact alone they obtain a (publishers) copyright on the pieces involved. This copyright only restricts copying of their layouts/arrangements, for 25 years.
Assuming they have done some work to make these available in this format then good luck to them, but if anyone can find the originals they can copy them.
This is similar to the position with some of the 'Great' church music. (Messiah, Creation, etc.,) The 'big' publishers (Novello &c.) re-print every 20 years or so, with slight changes to layout, and possibly a couple of slight changes to the music.
This prevents you buying a single modern copy and running off enough copies for a choir. You will also probably want everyone to sing from the same edition. BUT... if you have an old (out of copyright) edition in good condition, there is nothing to stop you running off the required copies from that.

Nigel