First, thanks for sharing—this is an insightful taxonomy. Second, to get into one detail, it seems indentured servitude has more variation and complexity than the description above captures:
Indentured servitude is a form of labor in which a person is contracted to work without salary for a specific number of years. The contract, called an “indenture”, may be entered voluntarily for a prepaid lump sum, as payment for some good or service (e.g. travel), purported eventual compensation, or debt repayment. An indenture may also be imposed involuntarily as a judicial punishment. -Wikipedia
First, thanks for sharing—this is an insightful taxonomy. Second, to get into one detail, it seems indentured servitude has more variation and complexity than the description above captures: