The countries of travel will be stamped in their passport. Very easy to verify.
So you think ALL countries stamp your passport......not so....and please look at which countries do not......ooops.
http://en.wikipedia.org/wiki/Gallery_of_passport_stamps_by_country_or_territory
Also travel between adjacent countries do not even stamp passports, so my daughter while visiting Spain crossed over by ferry to Morocco and could have traveled through most of Africa without EVER having her passport stamped in Africa, and returned from Spain. Do people even understand international travel and how virus has no affinity from hopping on planes from anywhere to anywhere, and that the idea of stopping all air travel would stop the virus for awhile, but international business would still be conducted and people would travel by rail, boat, and automobile. By the way have you ever had your passport stamped going to Canada or Mexico.....Ever take a cruise and have your passport stamped while on shore leave.........not as simple as the talking heads make it seem, nor necessary with a virus with this low level of transmission.