>>58520513That's fair enough reasoning, but "it was created 20 years ago" is almost certainly referring to the real-life time since Gen 1 as of Gen 7, and the FR entry doesn't necessarily imply that it was only just recently created.
And as
>>58520639 points out, the Pokédex also has information like "Lunatone was discovered 40 years ago" being stated in Gen 3, Gen 2, Gen 6 and Gen 8. These can't all be true at the same time, certainly not over a period of more than a decade.
I think the OP image is accurate enough but in a franchise as big and that has gone on as long as this, with many changes to the setting and continuity never really being the top priority, there's going to be gaps and contradictions no matter what.
The biggest gray area is between Gen 2/4 and 5, we can't really say more than "at least 5 years, probably" based on the Team Rocket Grunt settling down in Unova and having a young kid between games.