WHO Were the Three That Month??

In the opening scene of "Tennessee Ernie Visits", Lucy reads her mother's letter, stating
that Cousin Ernie is on his way to see the Ricardos. Here, Ricky laments "That makes
three of them this month! Why can't people stay home anymore?"

This line has always struck me as odd. While it must be a "throwaway line", it feels as
though the writers are referring to characters who were on the show recently. But
there aren't any! Characters like Mr. Beecher and Barney Kurtz come later, so obviously,
Ricky is referring to off-screen characters who visited that month.

Like I've always written, not everything that happened to these characters is captured in
an episode, but the line makes it FEEL as if we missed something. Odd line, no matter
how you slice it.