When should you use this function? I know what the documentation says, but it means nothing to me:

Special version of getBlock to be used when you want to garentee the ID you get is below 256 This should ONLY be used by mods who do low level terrain generation, or ones that add new biomes. EXA: ExtraBiomesXL Specifically, if your block is used BEFORE the Chunk is created, and placed in the terrain byte array directly. If you add a new biome and you set the top/filler block, they need to be <256, nothing else. If you're adding a new ore, DON'T call this function. Normal mods such as '50 new ores' do not need to be below 256 so should use the normal getBlock

 

The only world generation I add currently/plan to add, is a single new species of flower. I ran some tests having it's ID in the 4000 range, and it IS placing it in the world; however, it is not consistent in the frequency, like it was while testing with the ID at 255 (can't tell if the two events were just a coincidence yet). Does a new variety of flower count as "low level terrain generation"?

That basically didn't help at all, but I'm going to assume that you meant I'm OK to leave the block value at 4000. Also, I think it should be known that I do in fact understand the fact that bytes are an 8-bit storage method, and that integers are 32-bit, I also understand what that means. However, saying that these have to do this, without really specifying further, is no better than every mom's favorite phrase: "Because I said so".

Terrain IDs (<256) are reserved for PRE chunk blocks.

If you use setBlockID or anything like that then you DONT need a terrain id.

However, if you're a biome, you need < 256

Things that are added to a byte array that is used in the chunk constructor need to stay within a byte.

Basically since your shit is working with ids > 256 then you should NOT use ids < 256.