The way I remember the Pokerap actually admits there may be more than 150... So it was never really canon even then that 150 was the limit.
Because how I remember it was something like this:
"Cause there's One Hundred and fifty, And MORE TO SEE."
I took that to mean that... Yep... There's more than that, we just haven't discovered the little critters yet.
...
And as for the Digimon discussion, I still like Digimon, and the series still is good... But it wasn't in the sense of it being higher entertainment.
In no Particular order... My opinion of each Season.
Season Three was the most the most Cereberal. Season One was the most Cohesive. Season Two was... Okay I guess... Season Four is the one I remember as "The one where the Good Guys don't win until everything is FUBAR". Season Five was were they started appealing to the Awesome Factor BY HAVING A HUMAN GUY CONSTANTLY PUNCHING MONSTERS IN THE FACE! And Season Six was an Excercise in Serial Escalation with a side of Nostalgia Panda Rings.
And The Hunters Arc?
It was... A Mess... An Enjoyable mess, like watching a Car Crash where everyone survives just because one of them is too Brave and Stupid to Die. And Emerging from the wreckage this boy who may as well be Ash Ketcham but isn't Swears to somehow Save the World by becoming the best Monster Hunter Ever and then he spontaneously bursts into flames.
...It pays not to think of the Hunters Arc as a Digimon Season... And to think of it more as what it would be like if Gurren Lagann was combined with Pokemon.
...
And Back to Pokemon... I always kind of assume that the Pokedex not being Updated for the New Region yet has Something to do with each new Region only just growing to the level of Human Development as the last. And Before that point, they haven't compiled each Region's Findings with the previous.
For example... Going from Kanto to Johto, the Pokedex is still brand new, and is a Product of Kanto, and Johto hasn't started cataloging Pokemon since they only just got the device they need to do so: A Pokedex Shipped in from Kanto. Which they didn't yet have the Know how to Make themselves from Scratch... And So they add in a new memory pack, and hope like heck that their Haphasard Solution will work, send out a few Teens, and Bring the Results back to the Lab, then ship the findings back to Kanto Somehow.
Onward to Hoenn, a few years later Kanto makes contact with them, a few Skips over to such a Degree that Kanto may not have even explored that far themselves before then, and they tell them their plan of Cataloging Pokemon. Hoenn has better know how than Johto, so they Cobble Together their own Pokedex, the first "Regional Dex", since they don't want to bother waiting for a shipment from Kanto. And once done, they contact Kanto, send over the findings, and after a bit of sifting, they add the findings together and call it the "National Dex".
...We Can Assume a similar story happens with Sinnoh...
Unova on the other hand may have Come up with the idea of a Pokedex Independently, having come up with it several years after Kanto did, and the National Dex came to them when they find out its already out there by word of Intrepid Explorers who find their land.
...And Finally Kalos... Who Just couldn't Get their stuff together in one Unified Pokedex, having had a freaking awesome one for ages but had Three Competing Indexes and no centralized research to list them on a single system. And it only being when Kanto makes contact that they finally decide on a unified order for their unique pokemon.
So the basic narrative of Pokemon's Human Civilization can be interpreted as people sitting their asses down in one spot and making huge assets of technology but only recently has the idea of "Exploration" even occurred to them, to the point they may have forgotten there were other civilizations out there with technology as good as theirs, that they just weren't able to communicate with. After all... The end of their maps may as well say "Out there be Dragons" and it being just a simple fact that means "There are literally Dragons over here, probably a Dragonite to be precise, they don't like you going that way, Please turn back. You have nice and comfortable Heating in you small island that you are holed up in."
...Damn... Should have started with that... Oh well.