Exceptions and Oddities, part 1

As mentioned previously, the men's duty trousers closed in the front via an invisible zipper. 

However, the women's duty trousers were, as best we can tell, always sewn onto the appropriate undergarment (DS9/NEM division shirt, VOY "female hero undershirt," the various T-shirts and tank tops, etc.), forming garment that was technically a jumpsuit but appeared to be two separate garments. 

In other words, the pants were sewn to the undershirt, forming a jumpsuit that just looked like the wearer was wearing pants with the shirt tucked in. 

As you can see, the women's duty trousers did not have a visible zipper pull at the top of the center front like the men's duty trousers did:

VOY, 6x25 "The Haunting of Deck Twelve"

The women's "duty trousers + undershirt jumpsuits" closed in the back via an invisible zipper:

Lieutenant Neely (DS9, 6x2 "Rocks and Shoals"

Jadzia

Janeway

Jadzia

These weren't just one-offs; (nearly?) every auction listing we've seen for a Janeway "2-piece" specified that the duty trousers and undershirts were sewn together, forming a jumpsuit: 

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