Depends on your definition of organelle (whether you limit it to plastids/mitochondria, both of which were derived from external independent living cells, or us

Depends on your definition of organelle (whether you limit it to plastids/mitochondria, both of which were derived from external independent living cells, or use a more expansive definition that includes more cell compartments that weren't derived from independent living cells). General acceptance of the endosymbiont theory is a relatively recent (much less than 50 years) phenomenon.