Complex sentence: In the ~ 70 years since his work, the number of known Local Group members has increased from his initial twelve to thirty-six as of 2003, by way of the discovery of almost two dozen low-luminosity galaxies.
Split into simpler sentences: In the ~ 70 years since his work, the number of known Local Group members has increased from his initial 12 to 36 in 2003. This was by way of almost two dozen low-luminosity galaxies.