Malcolm wrote: There is in fact no true standard set of Buddhist doctrines that universally apply to all instances of what we call Buddhism.
How did you determine this?
There are, in fact, four basic tenets common to all schools of Buddhism.
They are commonly referred to as the Four Seals:
All conditioned phenomena are impermanent.
The nature of conditioned phenomena is suffering (duhhka)
All phenomena lack inherent existence
The true nature of the mind is free from suffering (nirvana)
I think, this has been pretty consistent for 2500 years or so.
Any teaching that contradicts these cannot be called a valid Buddhist teaching.
Of course, anybody can claim to be an authentic buddhist teacher and make up anything they want,
but that doesn't mean they are, and If someone claims to be a teacher of Buddhism,
and teaches the opposite of these four,
then they cannot be regarded as an authentic teacher.
Likewise, not all Buddhists believe exactly the same things,
there are things that some schools teach that other do not
and "What buddhism teaches" and "What buddhists believe" is not always the same thing.