Not sure when Dutchmaid went out of business, but living about 45 minutes from Ephrata, where they were located, I run across their items once in awhile. They were, I think, one of the major home party apparel companies in their time, at least up through maybe the the early 70s (maybe mid, as I think your darling set is mid 70s). And I very vaguely remember the name from when I was a kid, probably from TV or magazine ads. I haven't found anything after that 70's timeframe. And though they're well known for lingerie, I've seen casual dresses and adorable tops from them. They must have been very much like Beeline--nice-quality items, if not "fashion forward," but that wore like iron. I have a couple of slips--a woven nylon satin and a cotton one, and they are both beautiful and in wonderful condition.
Wish I could tell you more about the timeframe they were in business, but even people around here seem to not know much about them. They know the name, but can't tell you a lot about the company.