I wondered if the people in the photos were models or actual guests.

If these photos had been made nowadays it would be obvious they are models, because nobody in the shots of the pool is overweight, except maybe the guy in the red tie who appears in the background in the postcard and the photo after it, and the man standing next to the slide in that photo--his belly slightly overhangs his swim suit.

But back when these were taken...it was actually plausible to naturally find a half dozen people at a pool with none of them overweight.

Upon further examination...definitely models. The photo in the postcard and the photo following were clearly taken at very different times, but the foreground women are the same in both. Same faces. Same hair colors and styles. Same swim suits.

How do we know the photos are well separated in time?

First, we see that the slides are on opposite sides...but that could be explained by one of the photos being flipped. That was not uncommon in print. It could also be explained by their actually being two slides, and we only see one due to the angle of the shot. So forget the slides for now.

Second, we see that the Moon House seems to be in a different position. In the postcard it appears that if someone swam straight out from the edge of the pool nearest the camera to the opposite edge, climbed straight out, and continued walking in that direction, they would pass the Moon House on their left. It would not in any way obstruct them no matter where they started on the near side.

In the photo, it appears that for most starting locations on the near side doing the above would run them smack dab into the Moon House.

If there are really two slides...maybe we can explain the apparent Moon House position by different shot angles, but not if there is only one slide with a flipped photo...but we can settle the Moon House issue without having to figure out the slide thing.

In each photo consider the diagonal line that goes through the corner nearest the slide and through the opposite corner. (The pool is not actually a quadrilateral, but is close enough that it should be clear what line I'm talking about). Also consider the other diagonal, the one that goes through the corner that would be nearest the hidden slide. Together these two diagonals form a cone.

In the postcard, the Moon House is outside the cone. In the photo, it is inside the cone. No mere change in shot angle or flipping of photos can change inside/outside cone. That's an invariant.

Conclusion: the Moon House moved between the photos, suggesting the photos were taken well apart.

(BTW, neither photo is flipped. Farther down is a third photo showing the pool and motel, and you can see that from the point of view of the pool looking toward the motel the motel extends far to the right, with little extent to the left. In the postcard, we can see that the motel does not extend far to the left. In the photo, we can see that it does extend far to the right. This shows that the postcard is not flipped relative to the photo).

(We still don't have enough to figure out if there are one or two slides. There are two if they haven't been moving slides. But these are people who can move Moon Houses! To them moving a slide would be child's play, so it is quite possible that the renovation that pool area renovation that moved the Moon House also moved the slide).