"Red" Designation For Copper Cents

I have been interested in large Canadian copper cents for quite a while now, although I only recently started looking into slabbed large cents of higher grades. In the process of trying to find ones with good eye appeal, I ran into a couple of questions.

1. The "red," "red/brown," "trace red" designations. After looking at a couple of ICCS coins and comparing them to those on the PCGS population report, I got the feeling that PCGS tends to be much more conservative in naming a coin "red." Are these designations based on quantifiable parameters, like the percentage of original lustre?

2. Changes to eye appeal after prolonged storage inside holders. I know that TPG companies advertise how they use inert materials in their coin holders, but in my understanding, this by no means that there won't be trapped gases to prevent further oxidation. Is it common for coins graded with the "red" designation to graduation turn brown over time? (My guess is that, if the holders are completely airtight, the chemical reactions might just reach equilibrium at some point, but I am only speculating because I don't have any real-life experience in this area).

Combining the two questions above, I wasn't sure whether ICCS just had a more lenient standard for "red" designations, or if their holders were just less well-built for whatever reason.

A couple of years ago, when the Landon collection came out, I followed a thread on this forum quite closely. I remember that many Victorian and Edwardian large cents were advertised to have at least 90% of original lustre. I would be very interested to know whether these coins, over the course of the past eight or so years, have evolved in their eye appeal.

== Edit: As Silver101 pointed out,3I mixed up the terms lustre and toning. In my post above I meant "toning." ==