They played a new edition of the work. I summarize what was in the booklet they gave us with notes from Olga Konovalova;
The VP of the Chœur classique de Montréal heard a 1970s recording from the USSR and the board and Louis Lavigueur liked it. The score for the choir and piano accompaniment were in the public domain. They got a copy of the score from a Russian choir that had performed it and Louis Lavigueur noticed differences between the choral scores and what they got from Russia. That's when they found out that there were two versions of the work. The first was used for the funeral of the King of Poland in 1798. The second is longer with a different orchestration used for the funeral of Tsar Alexander I. They then found the digitized 1798 edition's orchestral score in a Polish national library. The manuscript of the 2nd edition from 1826 was found in the library at the D. Shostakovich Philharmonia in St Petersburg. Kozlovsky did not have time to finalize the second version. The manuscript has notes from the composer suggesting that excerpts from requiems by Salieri and Cherubini be used in some places. They confirmed that the recording was the 1826 version without the unfinished parts. They decided to reconstruct the work. Two Russian technicians did it in Russia with the supervision of Louis Lavigueur on skype.
The VP of the Chœur classique de Montréal heard a 1970s recording from the USSR and the board and Louis Lavigueur liked it. The score for the choir and piano accompaniment were in the public domain. They got a copy of the score from a Russian choir that had performed it and Louis Lavigueur noticed differences between the choral scores and what they got from Russia. That's when they found out that there were two versions of the work. The first was used for the funeral of the King of Poland in 1798. The second is longer with a different orchestration used for the funeral of Tsar Alexander I. They then found the digitized 1798 edition's orchestral score in a Polish national library. The manuscript of the 2nd edition from 1826 was found in the library at the D. Shostakovich Philharmonia in St Petersburg. Kozlovsky did not have time to finalize the second version. The manuscript has notes from the composer suggesting that excerpts from requiems by Salieri and Cherubini be used in some places. They confirmed that the recording was the 1826 version without the unfinished parts. They decided to reconstruct the work. Two Russian technicians did it in Russia with the supervision of Louis Lavigueur on skype.