JohnBrowning
Good post.
You sum it up clearly that there are different manufactured filters under the same brand name.
Part of that is that it costs so much to ship filters across the ocean that engine companies and OEM's look for local sourcing.
That's not to say, based on volume, that certain part numbers will always be built locally.
For instance, Toyota has a design change ( as they seem to do every two years). The OEM filter will be of one type. Yet "locals" will find a filter that "works", rather than pay OEM pricing.
Generally the Japanese either change the height of the can or move the gasket inboard or back to an outboard design. Aftermarket filter companies play catch up to manufacture a filter that is of the same dimensions, etc as the OEM one. ( Well that's what happened in the past. Now companies will fudge if they have something that is "close enough" rather than tool up for one that is within mm of the OEM one. But i've digressed).
The other factor in filter manufacturing that you touched on is the media itself.
Globally there are 100's of medias to choose from. Performance wise you can find medias that perform simillarly but look much different, if you ever cut the filters open.
So the newest whiz bang media touted by someone is nothing more than something every filter manufacturer knows about but have chosen a different route ( cost being one key factor) as to what they use.
Suppose there is a decent media in Europe. Any guesses how much it would cost to ship a container load over versus the same amount of rolls of media made in the USA? Yet, one can find a media which performs equally or better here.
There is not, as of now, the same --how do I put this--- level of sofistication in media's in certain parts of the world. This is due to the manufacturing equipment and costs. Let's just say in Thailand the average consumer doesn't want to pay the equivalent of $2 for a filter...nevermind $10.
Which means there are foreign alternatives that "work" but may not be of the same quality media wise as one might expect.
( Not that one might think that "exceptions" to OEM specs are allowed by the OEM's themselves in local markets.. ..nah that would never happen.
)