Methods, apparatus, systems and articles of manufacture are disclosed to optimize reference signature matching using watermark matching. An example disclosed herein includes selecting first unhashed reference signatures to evaluate for a second time segment of monitoring data based on watermark coverage of a first time segment of the monitoring data, the monitoring data obtained from a meter monitoring media presented by a media device and comparing the first unhashed reference signatures with first unhashed monitored signatures from the second time segment of the monitoring data. The example further includes, when a first media event associated with the monitoring data is not identifiable based on the comparing of the first of unhashed reference signatures with the first unhashed monitored signatures hashing the first unhashed monitored signatures to form a corresponding first hashed monitored signatures and comparing the first hashed monitored signatures with a library of reference hashed signatures to determine the first media event associated with the second time segment of the monitoring data.