The pie chart in 1.RV-Pre1 is very different than it is in newer versions. One notable difference is that each blockEntity is a string of three letters instead of it's name. Here is how to tell what block is loaded in by looking at the blockEntities tab.

The path to the blockEntities tab is still the same; "tick", "level", "entities", "blockEntities"

NOTE: "unspecified" is nothing. Ignore it. You probably already knew this.

NOTE 2: Each block is the same color on the pie chart; gray. The only exception to this is the "moving piston" block, which is grayish-green.

Useful stuff: aqk = Spawner aqg = Furnace aqx & apx = Chest (i don't know what differs from the two, aqx appears more often than apx in dungeons, and apx appears in jungle temples, desert temples and villages)

Tip: If aqk appears but aqx/apx does not, that means that the mob spawner loaded did not generate with chests, therefore rendering it useless.

Less useful stuff: aqi = Hopper aqa = Daylight sensor apw = Brewing stand aqo = Skull (this includes player heads and the dragon head) aqd = Enchantment table apu = Beacon aqe = Ender chest aqx [Green] = Moving piston (Note: Only shows when a piston is moving. Not when fully extended or not extended. However, if your pie chart is open when the piston is just activated [or just deactivated] aqx will stay open on the pie chart until you reload it.)

If I missed something (eg. a block) please let me know in the Discord server.