Is the volta ONLY used to mark unique end of a section or can it mark unique verse content within a section?

Question

I have a three verse, two chord song:

Verses 1 and 2 are

a b c
a b c
d d e

Verse three is

a b c
a b c
a f g
d d e

Without writing everything serially, within a repeated section with lyrics listed as:

• verse 1. Initial blah, blah blah tah dah
• verse 2. Similar blah blah blah, tah dah (that follows melody)
• verse 3. More of blah blah and inserted deed dee dee, then tah dah

What marks do I use to show the unique structure of V1 and V2, vs V3?
Do I use volta 1 2, volta 3, within the section?

Answer 1

Most standard approach

The most straightforward thing to do is to use one volta for the "normal" verse, and one volta for the "extended" verse.

|: a b c a b c || Volta 1 & 2 = d d e :|| Volta 3 = a f g d d e ||
Verse 1 lyrics    V1 lyrics cont.
Verse 2 lyrics    V2 lyrics cont.
Verse 3 lyrics                            V3 lyrics cont.

Less standard approach

Another option if the "inserted" section is short would be

Play 3x
|: a b c a b c [3rd x only: a f g] d d e :|

In the score, it would look something like this:

This is risky, however, as it's prone to confusion or mis-reading. It could be combined with a "to 'location'" mark to help clarify. This is loosely what pit musicians do, for example, when marking cuts in their scores. The cleanest options would be "to 'rehearsal letter'" (as below) or "to 'measure number'".

Special case

When only a small number of measures is involved, an ossia could be used.