Unreleased outtakes, demos and BBC sessions by The Beatles are expected to be made available on iTunes later.
The 59 tracks from 1963 are due to be released to stop them falling out of copyright and into the public domain.
EU copyright law covers recordings for 70 years if they have had an official release or 50 years if they have not.
Some fans have said the songs appeared on iTunes briefly earlier, but the BBC understands they will reappear later on Tuesday and remain indefinitely.
The collection includes four alternate takes of She Loves You, two of From Me To You and several live versions of Roll Over Beethoven.
It also features three attempts at There's A Place, as well as demos of two songs the group gave to other artists - Paul McCartney and John Lennon's acoustic version of Bad to Me and Lennon's piano demo of I'm in Love.
Many of the tracks come from BBC session recordings
The tracks had been widely bootlegged, but never officially released until now.
After a recent change in the law, the master tape for The Beatles' 1963 debut album Please Please Me is protected by copyright until 2033, but the unreleased session tapes for that album are not.
If the Beatles chose not to release the recordings before the end of the year, other record labels could theoretically put them out and profit from them next year.
The band's 1962 debut single Love Me Do arguably slipped out of copyright last year before the EU's copyright extension was signed into law.
At least one record company issued a "remastered" version of the song, although that has since been deleted.
The copyright law in question only covers the recordings - the composition of the songs remains the copyright of the songwriter for 70 years after his or her death.
The Beatles are not the first band to issue rare material in a bid to extend copyright.
Bob Dylan's record label rushed out 100 copies of an album last year containing early TV performances, alongside multiple versions of Blowin' in the Wind, Bob Dylan's Dream and I Shall Be Free.
Officially called The 50th Anniversary Collection, it carried a subtitle which explained its true purpose: The Copyright Extension Collection, Vol. 1.
A second volume followed this year, while Motown has also begun issuing rare recordings on iTunes under the "Motown Unreleased" banner.
