we've noticed from our personal logs and from logs from ESOlogs.com that the Spaulder doesn't apply the buff intelligently.
If we take one of the top public logs for a Yolnahkriin fight as an example:

This is what wearing 2 Spaulders looked like and:


This is what it looks like when you isolate for source.
You might say "well one of the wearers was the OT and they're not always in-group" and to that, I'd say that we have had a similar or worse experience while having 2 healers, 1 in each stack, wear the Spaulder.
You can try it, the results are reproducible. Our take on it is that the buff is not intelligent like the old PA was, and will apply to some people and will not apply or barely apply to others.