Observations on entity spawn ticks in minecraft forge 1.15

ObservationsOnEntitySpawnTicksInMinecraftForge115.txt

the world attempts to spawn monsters every tick
the world attempts to spawn animals every 400 ticks
entities classified as MISC are not spawned in world-chunk ticks

int mobCap = nominal cap * tracked chunks / 289D	// 289 == 17^2
	nominal cap is 70 for monsters, 10 for animals
	tracked chunks is the number of chunks tracked by any player (the range appears to be 8)
		I'm not sure if this is a square or a circle, but if it's a square, then we have 289 chunks tracked per player (minus overlaps)

if (total Explicitly Persistant Loaded Mobs < mobCap)
	attempt to spawn entities

an entity in a world is an Explicitly Persistant Loaded Mob if
	it is a MobEntity of the same classification as what we are attempting to spawn
	it is in a loaded chunk
	it is persistant or preventDespawn is true
		persistance is a serialized entity field that starts false for most entities, it becomes true if
			entity picks up an item or is equipped with an item by a dispenser
			some structures or features that have initial entities make them persistant
			entity is a skeleton horse or skeleton created by a skeleton trap
			entity is a villager that was formed through the curing of a zombie villager
			entity is an elder guardian
			entity is a Drowned formed by converting a zombie that was persistant
			entity is named by a nametag
			entity is a cat and spawns inside a swamp hunt (likely becomes persistant even if summoned or spawn-egged)
			entity is a zombie villager formed by a villager being killed by a zombie
			a cat entity becomes collared by a player
			entity is a slimeling spawned by a persistant slime
			entity is created with the nbt tag {"PersistanceRequired": true}
			-- if the entity's tag is set after it is created, it may not become persistant until data is read from its tag again
		preventDespawn is an entity method that usually returns false
			true for raiders during a raid and fish spawned from a bucket

it's worth noting here that most animals don't despawn naturally but are also not Explicitly Persistant
  and thus don't count toward the cap, unless I've missed something important
  
  i.e. animals prevent themselves from despawning by overriding canDespawn to return false,
    which doesn't seem to count it toward the Explicitly Persistant Loaded Mob cap