Yes, I remember that era. I did not follow figure skating very closely then. But, based on general info from our Olympic judge, in that period of IJS development the policy was that PCS should be tied to TES. So, the highest TES should automatically receive the highest PCS and if the TES was hurt, like, if skaters fell a lot, then their PCS should be lowered as well. According to this, Surya of 1991 would receive at least 8+ PCS, which would be of course... very fun. So they tweaked the rules once again and now the PCS is capped in case of falls but not very much and the highest TES does not guarantee the highest PCS. Although it's usually not far behind.Have to say it though ... there's a difference between skating skills improving, and a skater's skating skills MARKS increasing over time (which is often more about them skating cleanly rather than significant intra-season improvements.
Alina Zagitova's SS for her 2017 cup of China FS was 8.39, with no judge giving her 9's or higher. (https://www.isuresults.com/results/season1718/gpchn2017/gpchn2017_Ladies_FS_Scores.pdf). By the Olympics, her SS was 9.32 with every judge giving her 9's or higher. From November 3 to February 23, her skating skills did not improve from a grade of 83.9% to 93.2%. https://www.isuresults.com/results/season1718/owg2018/OWG2018_LadiesSingleSkating_FS_Scores.pdf
Lipnitskaia was 7.61 at Skate Canada (https://www.isuresults.com/results/gpcan2013/gpcan2013_Ladies_FS_Scores.pdf), and was 8.64 in the team event at the Olympics (https://www.isuresults.com/results/owg2014/owg14_TeamLadies_FS_F_Scores.pdf) - and 8.68 in the individual FS where she fell ( https://www.isuresults.com/results/owg2014/owg14_Ladies_FS_Scores.pdf - and just 8.75 for Mao Asada).
But this is not the discussion that this thread was created for - this thread was created to talk about skill difference that can be seen with an eye, not to analyze specific judges' marks or discuss how PCS should e awarded.
Can you bring up some video evidence and put a finger on if?I agree. But to the prior points, I do find that when a skater is not delivering the elements, or doesn't feel entirely comfortable out there, they start pushing off their toe, or their edges flatten. They skate with less "power/speed". They might miss exit and entrance transitions and leave out choreo that may reduce the "variety of edges/steps/turns/movements/directions" than they would otherwise exhibit if they were performing cleanly. They may sacrifice clarity of edge because they're just not into the performance/phone it in.

Like I said, this thread is not a discussion about how the PCS should be judged. However, in terms of skating skills that can be seen by an eye, this is a very interesting question: how much skating skills - or rather, the display of skating skills if we consider that a skill is something that a skater generally possesses - actually suffer when a skater has a bad day?
I'm more interested into what they want to say and what they want to be their legacy.