But the foundation does seem to be pretty clear and universal - if you have this ticket for 49€ a month, you will be allowed on all RE/RB/S trains, plus buses and trams. This alone is a fantastic deal for a lot of people. On top of that, some states will have some extra offers or additional forms of public transport with extra rules, but if you need to worry about that, then you needed to worry about that before the ticket anyway.
Sure it's not perfect, by far.
But it's a major improvement.
And you don't build a city in a day, you build it bit by bit incrementally.
For example yes, the 49€ ticket doesn't to allow you to take a dog or bicycle with you (consistently never; some metro trains just happen to not require tickets for dogs at all).
But would you prefer to have a 49€ ticket today, or wait another 3 years until they perfectly discussed out all the nitty bitty details of transporting things which are not humans but consume human sized space?
Instead you get the ticket today _while they work on a extension ticket for bicycle and dog transport_.
Similar yes there is a very small number of regional (non metro) lines which are labeled in a way where it seems to be valid (they are RE lines) but is not. But this is mainly the reason due to how exactly the contracts for this lines have been made. Contracts which get renewed every few years at which point you can either fix this or give them different names. Why should the ticket wait halve a year or more until all of the contracts are renewed just to fix this? (Also non of this lines are major line, they always have similar alternatives alternatives AFIK.)
It's like getting a good car for free and then complaining for days that the backseats are quite bit worn down, just ridiculous. Through they need to put a bit more work into providing easy to find informational materials IMHO.
Apart from that the ticket is valid in essentially every regional train. There are some weird cases that might not be valid, but those are as far as I understand some unusual edge cases and some of them are being negotiated. But this doesn't affect the vast majority of users.
it's not, which is one of the complains
there is a small number of RE trains which have contracts as if they are long distant trains and are operated by "DB Fernverkehr" (which normally operates IC,ICE trains) but are labeled as RE not IC/ICE..
but this will be fixed over time as the contracts a renewed, either by including the ticket or renaming the train as appropriate (the cases I'm aware of might be fixed in just a few month)
current exceptions I'm aware of are RE17, RE28, RE56 all stations on their line are also included in other lines and their where added as during rush hour parts of the exiting lines where just too over crowded
the problem is there is currently no sane way to check for what RE lines are special cases, but then AFIK this problems will likely be fixed very soon one way or another