Stereo Tool

The last standalone release of Perfect Declipper was 3.01 (April 12th 2017).

I'm wondering if that module of Stereo Tool has seen a lot of technical/quality improvement over the years, or is it essentially running on the same tech as the old one?

AFAIK, the actual declipper algorithm hasn't changed since then. However, the updated GUI version of PD is missing a few features and has some extra features the old one didn't. It's missing the final peak remover and Azimuth correction. However, it contains all the features in the Repair section of Stereo Tool such as the dequantizer and delossifier in addition to the rest.

I say it's worth grabbing and seeing if it fits your usage.

edit: Hm, I think I might have misread your question. You weren't asking about the new version of the "stand-alone" perfect declipper plugin after all?
Well, like I said, the algorithm hasn't changed, but the application in which it's hosted has improved.