“Whether the passage speaks of people collectively or individually...”
There is no doubt. It is not open to interpretation, since Paul is explicit. It is not talking about an individual’s sin:
“After all, who is Apollos? And who is Paul? We are simply God s servants, by whom you were led to believe. Each one of us does the work which the Lord gave him to do: I planted the seed, Apollos watered the plant, but it was God who made the plant grow...There is no difference between the one who plants and the one who waters; God will reward each one according to the work each has done. For we are partners working together for God, and you are God’s field. You are also God s building. Using the gift that God gave me, I did the work of an expert builder and laid the foundation, and someone else is building on it. But each of you must be careful how you build.”
That is the problem of Catholicism: It requires a Catholic to twist the plain meaning to fit an invented doctrine. There is NOTHING in this passage about an individual’s sin being only partially forgiven - which is also directly contrary to scripture:
“This is the covenant that I will make with them
After those days, says the Lord:
I will put My laws upon their heart,
And on their mind I will write them,”
He then says,
17 “And their sins and their lawless deeds
I will remember no more.”
- Hebrews 10
1 Corinthians 3 discusses Paula and others laboring to bring the Corinthian church to maturity, comparing the church to a field (first) and then to a building. And those who labor well will be rewarded, and those who labor poorly will not - although both will be saved.
But those who place tradition over scripture will also be dealt with:
“But false prophets also arose among the people, just as there will also be false teachers among you, who will secretly introduce destructive heresies, even denying the Master who bought them, bringing swift destruction upon themselves. 2 Many will follow their sensuality, and because of them the way of the truth will be maligned; 3 and in their greed they will exploit you with false words; their judgment from long ago is not idle, and their destruction is not asleep.” - 2 Peter 2
Even in that segment he is talking about "each one of us" doing the work "which the Lord gave him to do". These are the same individual works that are later found to be either noble (stone and metal) or inferior (stubble).
Note, too, that purgatory is not about mortal sin, just like this passage is not. It is about imperfections in our works that prevent us from entering heaven.
So no, no sale. When I see an interest in the Holy Scripture and not in sticking to Protestant theological fantasies I will pay attention to Protestant sniping at the Holy Church which you (collectively) left, to your (collective) shame.