> Consider the fact that, say, at the time when Verdi was rabidly popular, late 19th century, there was no iTunes, no TV, no CDs, cassettes, or vinyl records, and no music radio.

Notably though, there was sheet music as a mass-market form of music, so we can tell what was popular - and "opera tunes" definitely made the list, together with theme-and-variations sets based on opera tunes, medleys of opera tunes, parodies based on the tunes, arrangements for countless instruments etc.