W2W and Beatrix on a different forum have mentioned something about BSW.
Facts
Here is what we know i.e. these are facts that we know:
The official range of BSW is from 0.0 to 0.269999 (270k)
The reported notes are in the range 0.180000 to 0.269999 (90k)
It is believed that all the notes reported and in the SNDB in the above range have a Position Number (PN) of 51 to 59 i.e. the last or rightmost column (as viewed from the back) in a sheet of 5 columns x 9 rows.
When BoC was releasing these notes media photos showed sheets with BSW notes
Making Sense of Facts
Going by the PN and the range it would seem that the skip number of these notes is 10,000.
Given that PN 51 to 59 are printed in the range of Serial Numbers 0180000 to 0269999 it is simply not possible to assign the printing of other PNs from 91-99, 81-89, 71-79, 61-69 with a skip of 10,000 within a range of serial numbers 0000000 to 0179999.
This would suggest some special printing arrangement (could be the sheet size was not 5x9, could be that other spaces on the sheets may have been used to print something else etc.) not unusual for trial runs.
Given the above and given that BSW sheet was seen at the time of first release of these notes it is possible that even though alphabetically BSW is last, it was printed before any other prefix from BIE to BIZ and BSA to BSW. Something similar has been noted with FTH M-C, EKZ and FBB i.e. these prefixes have been used in the media during the first release of these notes and yet they have either been rarely found (FTH M-C, and EKZ) or have not been released (FBB) before other prefixes that were printed later (FTY, FTZ and FFA bundle straps show dates which are after the release)
Now for the most interesting clue. It is believed that the plates used to print the back of BSW was different than the plate used to print BIE to BIZ and BSA to BSV. I have not presented this evidence publicly yet but I will do so once I get a BSW is hand. I have presently based it on the images I have seen of these notes.
It is my belief that the BSW was first prefix to get printed and most likely used for final circulation trial.
Bottom Line
The total number of BSW's can be no more than 270,000 which is what the BoC has declared.
The BSW's that will be found are all likely with PN from 51-59 and I think the total will not be more than 90,000. There is evidence (which will be presented in due time) that there is identifiable difference in some aspect of printing found in the BSW compared to notes with PN 51-59 of all other prefixes BIE-BIZ and BSA to BSV. Given this I think BSW should be considered special from a collectors point of view.