[Tango-L] types of valses?

[anfractuoso anfractuoso]

Hello everybody,

I hope there is some interest in this, more musical, type of a question. I
did try to search the archives on this subject but could not find anything
useful.

How many types (sub-classes) of vals exist in tango and how do they differ
from each other?

For example, there is "vals boston". What is it in terms of what is
different from a regular vals?

Some other are more obvious - e.g. "vals viennese" (my designation) is a
tango vals that emulates a viennese waltz in certain characteristic
features. Examples exist by the Canaro and Rodriguez orchestras.

I am interested in real sub-classes of vals that one can identify based on
systematic features, and I am also interested in the different sub-classes
as labelled on sheet music. What I mean by this distinction is that
sometimes the sheet music labels do not mean anything different, sometimes
they do.