The surviving Beatles members reunited at London's O2 Arena on Thursday, Dec. 19

The Grammy-winner performed his 1979 holiday classic during a concert in Manchester, England, on Dec. 14

At the time, Carpenter thought McCartney was "young" and "only like 10 years older than me"

David Tedeschi's Disney+ documentary draws from newly unearthed footage, offering an intimate glimpse of how the band conquered the country