A lot of this is personal perception vs "name" recognition. Most people who buy tickets to see the Mormon Tabernacle Choir, or the Boys' Choir of Harlem, probably have no idea of any one singer's name, but you have a "percepetion" of what kind of musical style you'll hear onstage. On the other hand you have a group called "Peter, Paul & Mary" -this is name recognition, because each individual in the group is specifically named, and any substitution would make them no longer the group one paid to hear.
When Pete Seeger left the Weavers they carried on with various folks in Pete's place (Erik Darling, Frank Hamilton, etc.) and were still the Weavers. And everybody knew what they would hear at their concerts.
At the end of the day, there's no deception being practised here; Bob Shane has come right out and said that he won't be able to perform onstage for awehile, and those who are still Kingston Trio fans, who loyally continue to buy their records and attend their concerts, are probably going to show up regardless of who's in the group; folks who are *not* K3 fans probably won't care either way.

Mary Katherine