There was a further problem with the random splitting if the units between the two sides. You could be Nat. Spain and have some Divs in Republican territory. They would capture the province they were in but you would be surrounded by Republican territory and cut off from supplies.
That was only half of the problem. The event had two parts: the first part divided up existing divisions between the two sides, while the second part added more units in specific locations. Whoever controlled the province where they were placed got the additional troops. In several cases, the provinces where those additional troops were placed could end up in either country's hands, which meant that they could not only randomly get those units initially in the other side's province, along with the province, but get the additional troops intended for the other side as well.
I saw one SCW where the Republicans ended up with the airfield province where the Nationalist air units appear (Ferrol, or La Coruna?), so the Republicans got BOTH sides' airforces. The initial land combat went nicely for the Nationalists, but constant bombardment demolished and continued to suppress every single on-board IC point they had, as well as reducing the infrastructure of the cities to 0, so it took close to forever to repair. The Nationalists managed to capture all but the one Republican VP location (Mercia?), but eventually practically every unit ran out of supply completely, as well as reinforcements, losing any ability to advance or recover damage. When I checked, they were up to almost 20 Revolt Risk, totally out of Supplies, and unable to produce enough to cover even half of requirements, even without diverting anything to deal with the RR. The handful of remaining Republican units simply brushed them aside and took everything back without a fight. That was all due to air power based on an offshore island for part of the time. The Republicans won after almost 2 years, roughly 17-18 months of fighting and another 5-6 months of just advancing to take over the practically uncontested provinces, aside from the numerous Rebel spawns.
Another game ended up with several major Republican provinces going to the Nationalists, and about a quarter of the intended Republican army being added to the Nationalists instead. That turned into a Nationalist cakewalk and ended in under a month.