For what it's worth (I organize the bloodmobiles in our school)
Red Cross changed the guidelines for those who have been in European countries. I can't recall how it changed, but several who were declined before were not eligible.
Huge reason blood is in short supply this time of year: A very large proportion comes from high school bloodmobiles. Many schools are just now returning to school.
Curious though - why do you think they're going to need a lot of blood? What kinds of injuries are that widespread that require transfusions of plasma, red blood cells, or the whatchamacallits (forgot the third component)