> So, assuming the source material is correct and electrons indeed have mass, SSDs do get heavier with more data.

That is definitely wrong! No way the source material has more electrons. The only way it could do that is by being charged.

Richard Feynman, The Feynman Lectures: "If you were standing at arm's length from someone and each of you had one percent more electrons than protons, the repelling force would be incredible. How great? Enough to lift the Empire State Building? No! To lift Mount Everest? No! The repulsion would be enough to lift a "weight" equal to that of the entire earth!"

From: https://tycho.parkland.edu/cc/parkland/phy142/summer/lecture...