On balance with 5 Axis diplomatic chips in play at all times from September 1, 1939 it seems (to this non math guy) that Yugoslavia will only move about 44% (to aggregate of 89%) before DE 104 kicks in starting February 24, 1941. This will cost the Axis about 500 mpps plus the opportunity cost of receiving no income from Yugoslavia if it is conquered/occupied prior to February 1941 (typically it is).
Although an earlier writer extolled the value of turning Yugoslavia with diplomacy and receiving use of their infantry corps [and presumably not having to have the two garrisons], the math suggests that with average luck it is very unlikely that Yugoslavia will join the Axis before the coup that has a 50% chance of arriving after February 24, 1941 and presumably every turn thereafter.*
Have you ever seen Yugoslavia join the Axis due to diplomacy?
*I acknowledge that a writer also noted that Yugoslavia was still neutral in December 1942, but I don't know if the Allied player activated DE 104.
"L'audace, l'audace, toujours l'audace."