So, apparently 103 official citizens live during 2241 in Vault City. But why only 103? (Most) Vaults can hold up to 1000 people. Why are there about 150 years after Vault 8 opened only 103 official citizens left? (Actually, only 102, if you don't count Thomas Moore)

I mean, 90% of the Vault 8 Dwellers can't have spontaneously died or disappeared after it opened (assuming that Vault 8 had exactly 1000 dwellers). I also doubt that Vault 8 only had 100-200 dwellers. Does anyone have an explanation for that?

I think the issue was that the vault was originally low in population because most people thought it was just another drill when the great war actually happened, so fewer people made it to the vaults.