The closest analogy I can think of for PCEG is something like the League of Nations (as an attempt at world government) that fails. So, just as the League of Nations led to the UN, PCEG becomes the UEN. Would that be a fair assumption? With the PCEG Investigations post-Occupation (2065-2080), would that be something similar to the Nuremberg trials and CROWCASS in tone? Or is it more like the McCarthy era show trials ('Reds under the bed'), rooting out quislings? After its dissolution in 2070, how pervasive are PCEG ideas? Does PCEG become an historical artifact or do PCEG ideals remain a cultural identifier, long after PCEG is 'gone'? As an example, Guangdong was an enthusiastic part of PCEG (but not the UEN) (core 209). What would that mean for Venus colony laws and customs? Would they be 'draconian and unjust' like PCEG (core 208), versus the probably more liberal, individualist, or non-existent laws in Redland, run by criminal cartels?
Are the later Orion War protests on Venus (core 175) because Venus opposes any war with aliens? Or is it because the war with aliens is primarily a UEN initiative (a possible cultural hangover from Guangdong pro-PCEG/UEN antipathy, passed down as a cultural bias)? That could also lead to a distinction between the tone of protests during the period. Mass popular uprising based on a firmly held conviction (war with aliens is bad), similar to Vietnam era protests versus state-sponsored protests based on political and economic ideals (UEN bad, trade good- therefore, war bad). Or some combination of both?
That Hong Kong campaign sounds sweet! It's right at the boundary of "plenty of story hooks to draw from" and "not a lot of future canon depends on the details" that would give you a lot of freedom in a campaign like that.
re: Mars, I actually have a short story in my archive which is a log entry of an officer on the Mars colony. The Mars colony is not very large (I haven't pinned an exact number, but in the story cites 10 children born between 2056-2066, a birth rate which would probably put the number of colonists somewhere around 100-150 at the most), which might limit the variety of storylines in a long-running campaign. One possibility to keep it from getting stale might be to just start it during the isolation, timeskipping a few years each session and reestablishing contact by the third or fourth session, something like that.
The equatorial Occupation era campaign would almost certainly be the most straightforward campaign to run, as missions for the resistance can be easy to write, plan, and play without having to juggle a lot of interconnected plots. I have an adventure set in South America during that time which I run at conventions which is always a good time, and features characters who belong to the resistance cell that ultimately colonizes Redland. Similar adventures in Africa would be quite possible, there's just less written canon for that region - so, similar campaign styles but with different flavor and a little more freeform.
If you'd like, I'd be happy to email either the Mars short story or the South America adventure (such as it is - it's very incomplete at the moment as so far I'm the only one who's run it, but the goal is for it to be a published adventure module) to use as a starting point for your campaign.
League of Nations is an decent analogy, but it was inspired a little bit more by the US under the Articles of Confederation, prior to the Constitution. The main difference between PCEG and either of those was the intentionality, which is evident in the name: "Provisional". The PCEG was designed to be an interim government to deal with the aftermath of the Bactaran occupation, while diplomats met and discussed plans for a more stable longterm world government, which eventually became the UEN.
The investigations definitely started off like Nuremberg, and progressed more towards McCarthyism as time went on and the "low-hanging fruit" of collaborators was gone. The most distinctive "PCEG idea" that outlived the PCEG would be the drive for revenge against anyone who hinted at collaboration which (somewhat ironically given its origins) some in the Cascade States would champion as their cause later. The PCEG is definitely viewed as an artifact of the past, a necessary intermediate step between the occupation and a stable world government.
Guangdong didn't hold specific idealistic ties nor feuds to either the PCEG or the UEN, and joining one but not the other was simply a matter of economic practicality for the region. As such, Venus didn't inherit much of PCEG culture. Venus's opposition to the Orion War is very much because its tourism-centered culture has closer ties to aliens than those on Earth do, though the fact that Venus is independent from the UEN does make it easier to express those views.