R191: Varnish Bands, not Squares, and a Quadruple Surcharge

Like last Sunday, this post covers the final set of 1898 dollar value revenue stamps, but this time only quirks involving the $2 value.  In particular, quirks regarding the nature of the varnish applied to the stamps that received the wrong overprint, the overprint for the "gray" $2 stamp, #R185.  

What I'm calling a varnish band appears to occur across versions of R191 that have R185's numeral overprint, including R191a (single overprint) and R191d (triple overprint), and an unlisted R191 with  a quadruple overprint.  Examples of these 3 stamps are featured below.  As you may know, some, if not most examples of the normal versions of R190 to R194 have a square of varnish in the center of the stamps that underlays a numeral overprint to help foil cancel washing and reuse.

The post last Sunday on the tendency of these stamps to change color toward the hue of the R184 to R189 raised the prospect that the varnish square might be responsible for the color changes.  Whether that is the case or not, the question prompted David Thompson's inspection of his copy of R191a, a version of R191 with a single R185 type overprint.  He noted that the stamp does not have a varnish square but a varnish rectangle or band across the center of the stamp, and despite appearing unused, has no gum.  A scan of his stamp follows, along with a version that helps highlight the varnish "band":

So after Dave told me about his stamp, I looked at the only R191 I have that has the R185 overprint.  The stamp has the same varnish band, not square, appears unused, and has no gum.  It also happens to have a quadruple overprint, with a strong image to the upper north of the main overprint, a slightly weaker one on the right, and very weak image slightly above the main 2:

So with access to both my stamp and Dave's, I figured that despite the listing in Scott that these must really be printer's waste, produced in trials to sort out the application and the use of varnish.  That the BEP used the R185 overprint (maybe the R191 version wasn't ready yet) seemed to help me rationalize such a thought, 

But with a bit of extra digging, an example of R191d can be found for sale on Ebay by the seller buystamps.  In addition to the varnish "band", no gum, and an unused appearance, the stamp has what appears to be George Sloane's signature on the back, which for me speaks to the legitimacy of the oddly overprinted stamps.  Somewhere I have a copy George Sloane's book with his collected columns and with all my moves I can't locate it at the moment.  I'm wondering if he might have written about these stamps.  It would be good to know if he confirmed that they were regularly issued.

I have a few dozen stamps from this series in my collection which I'll need to scrutinize.  Meanwhile, this column has prompted me to examine the Scott listing for R191 and I have a couple of questions:

• Except for David's copy of R191a, I've never seen this stamp.  Scott has them priced at only $150 unused.  Where are they?  R192 missing its overprint seems very common in comparison.
• I've never seen R192b, a stamp with the R185 overprint that is printed in violet.  Where is this stamp?  By comparison to R191a it must be quite rare given its Scott value.