Best Practice for Orders vs. Cart Adds with Merchandised Variable

[jeff_bloomer]

Gigazelle​ and other Adobe Analytics eComm experts,

I'm looking for some guidance on how to BEST capture the data for a specific merchandised eVar.  If I capture a merchandised eVar in the products string throughout all cart adds and then the item is ordered, would it also be advisable to include that eVar in the purchase event, or, am I good to only capture it in cart additions?

In other words, can I still accurately track orders against those products having a specific merchandised variable captured only on cart adds, or, is it best to also include that value when I "submit" the order?

Thanks in advance!