Replaces 21500 (Belge 1950 / Belge Lambert 50). An alternative - Belge
1972 / Belgian Lambert 72 (code 31370) - was introduced in 2000 to use
the standard Lambert Conic Conformal (2SP) projection method (code
9802). EPSG recommends this alternative.
I cannot spot any differences to the EPSG registry.
Which source of information did you use?