Yes, it's vastly overused and misused. Due to this misuse, more and more buyers are confused as to what the term actually means. That's why it's important to not label non-couture items as couture.
I did some reading and it's pretty much a guarantee that your dress is ready to wear. I will post a paragraph below that talks about how Hirshleifer's was a huge success at the time with the emergence of ready to wear. Since Paul Hirshleifer stock primarily American designers but supplemented his shop with high end designs that he purchased in Europe, I would imagine that your dress has a good chance of being of European descent. That being said, since he purchased these for his shop in the US, it's pretty unlikely that they were ordered ahead and custom made for specific clients. It sounds like they were purchased specifically for the store.
Have you turned this dress inside out and looked for another tag? I would imagine that it may have used to have a designer tag in there somewhere if the dress is indeed designer. I will say one thing though, that your dress is likely a very high end design to be sold at this shop.
"AN AMERICAN FASHION IDENTITY
Indeed, after centuries of dependence on the dictates of Parisian fashion houses, Americans watched as the European couture industry shut down during World War II. It was during this unique window of opportunity that the ready-to-wear industry, an American phenomenon, stepped in to fill the fashion gap. Industrialized production methods and standardized sizings that led to the manufacture of clothing designed to fit a majority of the population supplanted professional tailors that provided clothing personally made to reflect individual measurements. The ready-to-wear industry, as it was called, brought with it a couture style and quality but a price-tag that made the clothing more affordable. From elegant eveningwear to casual sportswear and separates, from high-end gowns to less expensive goods, ready-to-wear changed the fashion industry in America, making fashion more accessible and spawning a host of new designers that Paul introduced at Hirshleifers. From names like Pauline Trigere, Rudy Gernreich, Ben Zuckerman with his coats and suits, Norman Norrell, Donald Brooks, Bill Blass, Stella Sloat, Ben Reig, Originala, Tiffeau Busch, James Galanos, Oscar del la Renta came stylish sportwear and elegant eveningwear with a uniquely American look and feel. Paul and Rose were able to position Hirshleifer’s to take advantage of this design renaissance.
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In addition to buying goods from designers on Seventh Avenue’s ready-to-wear market, Paul also traveled to Europe to supplement his collections with the finest in Parisian and Italian fashions. Believing that the high-end luxury market was relatively immune from the downturns of the economy, Paul invested his dollars in the purchase of very expensive goods that he then offered for sale. This was a potentially risky step, requiring strong conviction and a confidence in his vision. A talented and insightful businessman, Paul’s vision came to pass."
