The bug

Anything placed between 30 million and 32 million blocks out from Infdev to Beta 1.7.3 will become impossible to access/retrieve in versions Beta 1.8 and above, including the latest version (1.20.5-rc2).

It'd be expected that, for backwards compatibility and upgradability and such, things built by the player should remain accessible by them and not suddenly become inaccessible, however this is the case here.

How to reproduce

A world from Beta 1.7.3 is attached to this ticket.

1. Load this world in Beta 1.7.3
2. Note that the diamonds are accessible
3. Upgrade this world to the latest version

Expected results

The diamonds should still be accessible as they were in Beta 1.7.3.

Actual results

They are not.

How to fix

Push the world boundary out to at least 32 million blocks, like it used to be at before Beta 1.8. This should be doable by searching for every instance of 30 million in the game's code and changing them to 32 million, and any instances of 60 million (or 59,999,968) to 64 million (these will likely be world border-related). The weird ghost chunk behaviour present in older version is due to arbitrarily-coded chunk limit values, rather than any hard limits imposed by data types. This should make these blocks accessible once more.

It should be safe to expand the world to 33 million blocks out rather than 32 million, which would be preferable in this case. Starting in 1.14 and increasing in 1.17, the game only starts breaking at 33 and a half million due to lighting changes and such, so 33 million flat should be a better cutoff point.