so, i waited another year to go and have a look at this mysterious begonia, so i can examine the stem ;)..
and yes, i think now i am quite sure that this is B. angularis.
It grew very ungainly, tall thick stalk, lower leaves gone, nobody pruned it - it's AN UGLY THING!
the junior was much better looking. Judge for yourselves.


this is the stem - the plant is close to 5 feet! with leaves mostly on top. very leggy! and the beautiful distinct white veining became rather gray, almost unnoticeable.

this is the veining - burgundy ..and the last pretty aspect in my view.
@LAbegoniac, does it look right for a grown up plant?