I was looking more into PCI. I found that the company no longer exists and went through, evidently, different iterations. The history I found seems similar to ANACs. Here's what I found:
PCI (Photo-Certified Institute) is a Tier 2 service. The grade depends almost entirely on which label is in the slab.
The "Old Green" Label (10-Digit Serial Number)
• The Reputation: Generally respected. In the late 80s and early 90s, PCI was a legitimate competitor.
• The Grade: Their AU 50 from this era is often "solid." It might cross to a PCGS or NGC AU 50, or perhaps an XF 45.
• The Toning Quirk: These specific holders were known for having a high sulfur content in the paper inserts. Over decades, this caused the coins inside to tone naturally but rapidly. Many famous "rainbow" coins actually started in these green PCI slabs.
I don't know how accurate this is but it does seem to fit my coin. I am interested in this- maybe I should start a new topic to hear if anyone has experienced this or even heard of it.
Still on the fence with the return. It was not cheap.

