[BUG]: I stratified an already stratified model. The normalized equations do not seem right.

[pascaleproulx]

Describe the bug
I stratified an already stratified model. The normalized equations do not seem right.
S_00to04 was stratified by 3 groups (a, b, c). I created S_00to04_a, S_00to04_b, S_00to04_c. See equations that were used in the normalized option. I was expecting something like S_00to04_a / (S_00to04_a + S_00to04_b + S_00to04_c).

https://app.staging.terarium.ai/projects/1c6e1c59-f162-413a-b0c5-24d70f7b9e32/workflow/47541466-2c71-432f-8d71-7ed6cc7acf0e?operator=166d7321-b638-45e1-bbb3-235e69d1c86f

Screenshots

[jryu01]

I think there’s some ambiguity in how the variables are grouped and how the normalization equations should be derived.

For example, when you have just these variables:
• S_00to04_a
• S_00to04_b
• S_00to04_c

It’s unclear whether:
1. They represent a single variable (S_00to04) stratified into three groups (a, b, c).
2. They are three separate variables (S_a, S_b, S_c) with a single group (00to04).

Current implementation does 1

When we look at how the model is stratified in this example (https://app.staging.terarium.ai/projects/1c6e1c59-f162-413a-b0c5-24d70f7b9e32/workflow/47541466-2c71-432f-8d71-7ed6cc7acf0e?operator=166d7321-b638-45e1-bbb3-235e69d1c86f), variable S_00to04 is strafitied with groups a, b, c and if so, the derived equation seems correct with current implementation.