terminology - What is another word for 'pronoun' within this problem domain?

An excerpt from the the song "99 Bottles of Beer" would be the following two verses:

2 bottles of beer on the wall, 2 bottles of beer. Take one down

and pass it around, 1 bottle of beer on the wall.

1 bottle of beer on the wall, 1 bottle of beer. Take it down and
pass it around, no more bottles of beer on the wall.

As you can see from the words in bold, one difference between these verses is the word "one" and "it". These words are pronouns representing the thing that is being taken down.

I'm trying to come up with a term that generalizes this concept. One options would be to simply use the term "pronoun". In other words, the "pronoun" for the first example verse is "one" and the "pronoun" for the second example verse is "it".

However, I am wondering if anyone can come up with a term to generalize "it" and "one" that is more related to the domain of the "99 Bottles of Beer" song.

As an example, the second word in each verse is another difference between the two example verses. We have "bottle" and "bottles". In this case, we can generalize these terms to represent the "container" for the beginning of that verse.

The "container" for the beginning of first example verse is "bottles", and the "container" for the beginning of the second example verse is "bottle". The concept of a "container" is related to the problem domain. It would be less descriptive to generalize this difference as a "unit". It's still correct, but it seems less related to the "99 Bottles of Beer Song". It's too general.

I feel that "pronoun" is similar to "unit". It's too abstract. Is there a word that can be used instead of "pronoun" that is more closely related to the song? Similar to the way "container" is more closely related than "unit"?