Considering that Freddie did not finish recording Mother Love, it makes lot of sense that it was his last vocal recording. According to Justin Shirley Smith the sound engineer during those sessions, the vocals were recorded between May 13 and May 16:
""The dates were not always written down, but after searching through the labels on old boxes of reel to reel tape, Mr Shirley-Smith says it was definitely Mother Love, recorded between May 13 and 16 1991.""
But These Are The Days video was shooted in May 30 and we can hear his voice in the color video footage of the recording session when he talks to the band members and staff, so that's the last voice record of Freddie not singing.
https://www.telegraph.co.uk/culture/music/music-news/10486116/Inside-the-studio-where-Freddie-Mercury-sang-his-last-song.html
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