Bracketed second letter of word?

[Grumpy]

What do the second bracketed letters in "retreating," "the," and "to" indicate below? I've frequently encountered similar examples like these in others' writing. What exactly is meant by the use of brackets around the second letters of words?

A Southern reporter traveling with Forrest makes clear that the discrimination was deliberate: “Our troops maddened by the excitement, shot down the ret[r]eating Yankees, and not until they had attained t[h]e water’s edge and turned to beg for mercy, did any prisoners fall in [t]o our hands . . . .

Thank you.

[Beeesneees]

What is the context?
It looks as if the bracketed letters were missing in the original document and the brackets show that they have been replaced in the transcript.
_________________
"Inside every old person is a young person wondering what happened."
Terry Pratchett

[Grumpy]

In other words, something to this effect?

A Southern reporter traveling with Forrest makes clear that the discrimination was deliberate: “Our troops maddened by the excitement, shot down the reteating Yankees, and not until they had attained te water’s edge and turned to beg for mercy, did any prisoners fall in o our hands . . . .

[Grumpy]

Or:

... , did any prisoners fall in t our hands . . . .

(The 'o' might've been missing in the word 'to' in the original.)

[Grumpy]

Anybody agree with the bolded examples, which may explain this? How about an existing written error in transcripted text? The writer had indicated via use of bracketed letters that it didn't exist in the original, but wanted to correct the errors so the text made sense. Sound valid and logical?

[Beeesneees]

It's more likely that the original looked like this where letters became too faded to be read:
A Southern reporter traveling with Forrest makes clear that the discrimination was deliberate: “Our troops maddened by the excitement, shot down the ret eating Yankees, and not until they had attained t e water’s edge and turned to beg for mercy, did any prisoners fall in o our hands . . . .

To know the context would be useful. I find it hard to believe that in standard writing you have 'frequently encountered similar examples'.
_________________
"Inside every old person is a young person wondering what happened."
Terry Pratchett

[Dozy]

[Grumpy]

Yes, in very old newspaper articles (that've been 'touched up' with these interpolated bracketed letters).

[Beeesneees]

Then, hopefully, this has answered your question.
_________________
"Inside every old person is a young person wondering what happened."
Terry Pratchett