Here's my guess, but it's speculation, since I don't know the casino at all, personally.

Looking at the set of Waterfront chips in your scan, I'd say the 50p chip (Paulson H&C, hot-stamped) is the "odd man out" in that set.
The 25p looks like it belongs with the other denominations in type style and maker. My guess is that the 25p is a plain mold made by Bud Jones from the same era as the inlay chips with bigger denominations. Perhaps made as part of the original rack of chips, but not used, or was retired before you began frequenting the club?

If that's the case, the 50p was a newer (post-opening) order, and they bought a less expensive hot-stamp H&C rather than match the BJ plain mold in a 50p version.

As a comparison, here's scan (from Chip Guide) of a plain mold $1 Sharkey's chip. It was issued in 1991 (per TCR) around the same time that Bud Jones was producing the LOT/ROT versions of their chips. (For an example, see Bonanza Casino - Reno's $5 chip on the Chip Guide). Those are from the early 1990's also. In contrast the H&C mold of the 50p hot-stamp is newer than the early 1990's.