No matter where you place the WS game, the 200X to 20XX oddity remains. Since it's MM3 that first uses 20XX. But at the same time World3 continues to use 200X+a. Forte's presence simply dictates 20XX instead of 200X, though.
The +a could bring it over to the next decade, or the first X can be 0 as already stated, but there's no +anything for the in-game and manual story of RFWS, which agree on that game taking place in 200X. If you ignore that they say that, you're ignoring the game's canonically stated timeframe. On the other hand if we accept it then all previous dates in other games have to be 200X as well, which contradicts the statement of the 10 years having passed between 1 and 8, unless WS happens before 8, which contradicts it being a pseudo-sequel to R&F. To place it anywhere we have to turn a blind eye to something, there is no way around it.
I think we should give the WS game some credit though. Wily is 57 as of RnF, yet supposedly "10 years before 8" Wily and Light looked the exact same. They really aged badly if we're to believe 8...
Aged well, you mean. Anti-aging effects might have some stunning advances in their universe. The art styles of the main characters have changed many times over the years, leaving no consistent basis for comparison to count wrinkles. Just looking and guessing at how old someone appears isn't always a very concrete approach.
Ariga's megamix also seem to cooperate that not that many years have passed, what with Kalinka still looking in her teens, but slightly older than before. Of course, being a manga one never knows how much it applies to the games.
I take that to mean you're trying to judge Kalinka's appearance in Megamix from this one simplified style background picture?
Kalinka was actually supposed to be 9 in R4, making her 3 years shy of being a teenager back then, but if you think she looks to be in the middle to older teens like 16 or 17 as of R9 that's a good 7 or 8 years passed there. But, again, I don't think judging from the artwork is the best idea. Besides that Ariga has taken ample liberties with the game canon regardless.
Then there's the pre 1 backstory, were those ever said to be in 200X and not in 19XX? We know from EXE that Capcom does not shy away from overwriting our timeline with high tech innovations. Like Soul Server's existence 30 years before EXE5. It should be entirely possible that a robot like Blues would have been invented in 19XX.
Rock (pre-Rockman conversion) was built in 200X. I don't think anything gives a stated indication of Blues' birthyear, though Powered Up appears to suggestively liken it to 20XX with all the rest.
While it's certainly quite true that PB's timeline placement is "after 7", we must also take into account it's not necessarily "before 8." In the past things like Wily and Roll's designs would make it so. But 9 introduces a whole new interpretation of the canon by allowing retro designs after 8. Not to mention that PF also pulls off a post 8 game with retro designs. That's all to do with the unique nature of the arcade games. If things like PF and Soccer can get away with not including the chronologically previous game's robot masters, then PB can as well. Different from the GB games where the gameplay mechanics solidify the timeline.
Since PF did it years before, I don't think 9 can really be seen as breaking new ground when it comes to using retro clothing designs. But 9 did break all the gameplay mechanics rules, which is actually a step back as far as using the player's move list to solidify anything is concerned. The reasoning is less stable than before we had such a counterexample.
Taking PB from a strict story perspective, we must simply choose to keep it's connection with PF in tact.
Where the main games in the series build on each other storywise, it doesn't exclude the possibility of a game occurring in-between. There isn't a plot reason why nothing could have happened between PB and PF, unlike the way that 6 leads into 7.
The storyline of Bass' betrayal and Wily's attitude toward him also seem to correspond with a game closely related to PF and later than RnF. Wily was more than willing to have Forte alongside King, where he is discarding Forte for a new robot in PB and PF.
Wily was willing to say that King II was to work alongside Forte, when Wily was on the floor groveling to the muzzle of Forte's buster. Doesn't seem to have been his plan before it came to that, considering how Wily had ordered the first King to battle Forte not too long ago. A lot of fast talking to save face was going on there.
Not to mention, if Wily would have said he'd kill Forte using a new robot derived from studying Forte, you'd think the guy would be more reluctant to let Wily to his thing to him.
You'd think from the ending of R&F Forte would be reluctant to be worked on by Wily anyway, after Forte had refused the installation of a limiter chip, exposed Wily's initial intention to replace himself with King and went on to ignore Wily's order to attack Blues or try to save King II's plans. Nonetheless, all that seems to be forgotten come R9 with Forte getting tuned up by Wily, all going back to business as usual. They just seem to have the kind of relationship where they hash it out violently, betray one another, proclaim all manner of mutual disrespect... but still wind up taking care of one another when the chips are down, perhaps even depending on each other. Forte wanting to be the strongest, Wily wanting to build the strongest robot, both wanting Rockman defeated, Forte perhaps needing the maintenance Wily provides, while Forte makes good sometimes saving Wily from being caught or mangled. They have enough common ground there even if neither one can stand the other's ego. I do enjoy their twisted father/son relationship. In that respect it probably wouldn't matter so much who got betrayed by who and when, they can still come together again for the next round. They can work together after R&F. They can work together directly after PB. They can work together after PF. It's open to several possibilities.