I work in retail. Not in clothing retail, but AV/Electronics.
Product procurment is a guessing game, at best, until the containers with the product have cleared customs. Until those containers are cleared, they do not exist in this country. Manufacurers can 'guesstimate' ETAs, but you can't put anything in stone, until the goods are onshore.
Then once you get them through customs, they have to go to the manufacturer's warehouse here in the US, and then get sent out to regional warehouses, or retailers' warehouses.
You can guesstimate, but it really is an inexact science. And for most retailers, Store Managers are generally not in the communication loop with exact ETAs.
I know this isn't the answer you want, but this is how it is for my company