A lot of homemade crochet items do have linings in them as people couldn't ensure that the holes they created were going to end up in the right places, and protect their modesty. The manufactured crochet items usually worked the panels so that the denser stitching was around the areas you wanted to cover up such as the chest area.
To be honest though, in the early to mid 60s, the majority of crochet items were hand made. It really is very evry quick and easy to do once you get the hang of it, and when I first managed to do crochet stitches (it's one of those things where you can't do it at all, and then all of a sudden something clicks and you've got it) I made myself a whole crochet hat while watching a half hour TV show... so a whole hat in half an hour was my first attempt.
When you buy modern crochet items it's all the other way around (even if you are buying the 1990s Biba range), homemade items are without linings, and all the manufactured items have linings. Most people these days wouldn't know what to do if you created a "how do I wear this" problem, they just wouldn't buy the item. So modern crochet dresses have linings.