You're right FF, it came out in 1973.
Taken from Wikipedia:
"On 4 September 2020, the album was reissued and features never before released outtakes such as "Criss Cross", released as a music video on 9 July 2020, "Scarlet", featuring Jimmy Page, released as a music video on 8 August 2020, and "All the Rage"."
So, no special occasion, they just found some bonus tracks for it. Exile on Main St got the same treatment around a decade or so back iirc. Think it might also have topped the album chart, but I'm not 100% on that.