meaning of "current bound set" in 18.5.2

[Stephan Herrmann]

Here's another one regarding 18.5.2:

For most of this section the spec is careful in defining
which bounds are incorporated into which bound set,
building up a sequence of B1, B2 and B3.
(Note, that B2 is constructed only conditionally).

Then at the end of the 5th bullet, more bounds are said
to be incorporated with "the current bound set".

The use of B1 ... gives the impression we speak about
distinct sets, but my intuitive understanding suggests
we are instead speaking about *one* bound set that is
incrementally filled with more bounds as the analysis
proceeds.

If distinct sets are intended, than I'm missing
- any use of the constructed set B2
- a definition for "current bound set"

If accumulation into one bound set is intended,
then all talk of B1, B2, B3 seems to confuse more
than it helps, IMHO.

please clarify, thanks,
Stephan