Hi Daniel,
Good question!
No I don't have a brilliant method of denoting new plugins in the Index Sorry, but I will think about it. What I'll do for future versions of the PDF is color code the newly added plugins.
As a workaround, you can (almost always) use the topic number as a guide to release date. In this version of the Index, the first plugin added was PdnFF, topic number 20380. Any plugin with a topic number larger than 20380 should be a new addition to the list. This method falls down when a plugin is first released in the Plugin Developers forum, and subsequently moved (screws up the topic number by retaining the first post topic number).
Just for you, the new Plugins were:
PdnFF
Average Edge Blur
PS Emboss
Liquify
Trail (originally missed from the list due to the hiccup mentioned above)
Night Vision
Thermal Heat Map
PSFiltersPDN