It's really hard to know what goes on with vehicle spawns.
Remember that some spawns are triggered when a near flag is flipped by the other team when one of the slots isn't spawned in the world. Easiest way to observe this is when Germans lose their A gimme, or Brits lose their F gimme on Amiens. Generally will trigger a vehicle spawn.
Rapid flipping of flags in combination of the tanks going down fast can trigger multiple spawns in short order.
This post has been edited 1 times, last edit by "tankmayvin" (Feb 27th 2018, 7:34pm)