Does Paired Pulse Depression Indicate a Lower or Higher Release Probability? And How?

I'm trying to understand the link between Paired Pulse Depression and Release Probability. There are a number of papers such as (Zucker & Regehr, 2002) which state that Paired Pulse Depression (PPR<1) should indicate a high release probability. And there are papers such as (Chen, Nobutoshi Harata and Tsien, 2004) which state that Paired Pulse Depression should indicate a lower release probability, owing to the exhaustion Ca2+ levels when generating the second postsynaptic response.

I'm not sure if I'm interpreting these papers in the wrong way. From my knowledge (I'm fairly new to electrophysiology), it would make sense that Paired Pulse Depression would cause a reduction in release probability. However, if the opposite is true, I hope to understand how.