I'm not sure where you're going with "both abstract and concrete", but
this doesn't seem to be the main point which hinges on universal.
The example of the worker, is applying universal as "Every", which is
a weaker version of universal as "princicple".
Both "every" and "principle" are abstractions, yes.
Measurements are abstractions.
The principle of dialectics is also an abstraction.
But the original quote is perfectly accordant with Marx.
One moves from an empirical (abstract) appreciation to a dialectic one
(concrete).
In other words, the universal in the quote refers to the principle by
which one attains the concrete.
Lenin is referring to process (methods), Marx is referring to form.
They are referring to the same thing.
The parts about context and experience I am happy with. However, we
have a caveat for the contextual truths and that is that principals
(universals) should apply across our historical contexts, what was a
principal (universal) then will still be a principal now.
I am perfectly happy with the description of concrete and abstract in
the glossary on the Marxists site:
http://www.marxists.org/glossary/terms/a/b.htm#abstract
Abstract and Concrete
Abstract and Concrete are philosophical concepts concerned with the
development of conceptual knowledge. An understanding of what is meant
by “abstract” and “concrete” is vital to making sense of dialectics.
For Hegel and for Marx, the contrast between abstract and concrete
<http://www.marxists.org/reference/archive/hegel/works/hl/hlnotion.htm#HL3_587a>
does NOT mean the contrast between an idea and reality. Rather ‘A
concrete concept is the combination of many abstractions’. A concept,
such as a number or a definition, is very abstract because it
indicates just one of millions of the aspects that a concrete thing
has, or a brand new idea which has not yet accrued nuances and
associations. Concepts are the more concrete the more connections they
have. If we say “The British working class are those who work for a
wage and live in the UK,” then we've made a very /abstract/ concept.
To make it more concrete is to show the many aspects of it; showing
the historical circumstances of its rise and development, the state of
the world it developed in, etc.
Huw