Features Get Corrupted Importing

CS-cart version:4.11.2

We have two related feature fields for each of the garments in our store:

Size: [Variations as one product][Dropdown list]

Size is the published size of a garment, eg : 2-3 years, 2-4 years, 3-5 years, 4 years etc. These include overlapping sizes because the various brands we stock have different ranges of ages that their garments fit.

Ageselector: [Product search via filters][Multiple Checkboxes]

Ageselector is intended for filtering eg: 2 years, 3 years, 4 years , 5 years etc. This is so that a customer looking just for items to fit a 4 year old can filter to show only products that have a Size range that includes 4 years.

An example of the import file includes the following fields:

"Product Code", "Variation group code", "Size", "AgeSelector"

"Product-A-2-3", "Product-A", "2-3 years", "2 years///3 years"
"Product-A-3-4", "Product-A", "3-4 years", "3 years///4 years"
"Product-A-4-5", "Product-A", "4-5 years", "4 years///5 years"
"Product-B-1-3", "Product-B", "1-3 years", "1 years///2 years///3 years"
"Product-B-4-7", "Product-B", "4-7 years", "4 years///5 years///6 years///7 years"

When this is imported the data in AgeSelector field is only populated from the first product from each product group, i.e. the result is as though we imported this instead:

"Product Code", "Variation group code", "Size", "AgeSelector"

"Product-A-2-3", "Product-A", "2-3 years", "2 years///3 years"
"Product-A-3-4", "Product-A", "3-4 years","2 years///3 years"
"Product-A-4-5", "Product-A", "4-5 years","2 years///3 years"
"Product-B-1-3", "Product-B", "1-3 years","1 years///2 years///3 years"
"Product-B-4-7", "Product-B", "4-7 years","1 years///2 years///3 years"

Even if I disband the Variation group the data is corrupted in the same way.

The only workaround I can think of is the following:

"Product Code", "Variation group code", "Size", "AgeSelector"

"Product-A-2-3", "Product-A", "2-3 years", "2 years///3 years///4 years///5 years"
"Product-A-3-4", "Product-A", "3-4 years", "2 years///3 years///4 years///5 years"
"Product-A-4-5", "Product-A", "4-5 years", "2 years///3 years///4 years///5 years"
"Product-B-1-3", "Product-B", "1-3 years", "1 years///2 years///3 years///4 years///5 years///6 years///7 years"
"Product-B-4-7", "Product-B", "4-7 years", "1 years///2 years///3 years///4 years///5 years///6 years///7 years"
But this causes products that are not in stock to be shown to a customer.
Is there a more elegant way to achieve this ?