Just discovered this thread and boy do I need my schooling cap on!
There is no such thing as VMRO pre-1913. The organization was called VMORO: Internal Macedonian Adrianople Revolutionary Organization. It covered the areas of Vardar Macedonia, Aegean Thrace and Adrianople.
Pretty much every member of the VMORO studied in Bulgaria, worked as teacher in Bulgarian schools in the Ottoman Empire (hello, Gotse Delchev), and also served in the Bulgarian army.
Until 1907, Bulgaria was still a vassal of the Ottoman Empire. The goal of an autonomous Macedonia was a long-play that would've basically been a repeat of this
previous Bulgarian Unification.
During WW1 what remained of the revolutionary organization was oficially integrated into the Bulgarian army. After WW1, it split into several organizations that covered the lands lost by Bulgaria: VMRO in Macedonia/Yugoslavia, VTRO in Thrace/Greece and VDRO in Dobrogea/Romania.
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My main point is, be very mindful when navigating this time period. North Macedonian historians have a tendency of employing massive revisionist history for political reasons.