I understand that although the basic composition remains the same, the phosphor ink from the new supplier is not as bright as that used previously. (I've been told that on some examples of stamps or Post and Go Faststamps the brighter phosphor had taken on a yellow tinge over time, which may be the reason for the change of supplier !)
First things first, this change was made in the autumn of 2015, so all printings with 2016 year codes have dull phosphor. The following stamps with 2015 year codes exist with both bright and dull phosphor. In the case of counter sheets all printings after the date shown are dull.
1st purple 18/09/15
1st Large 01/10/15
2nd class 29/09/15
2nd Large 03/09/15
1st Signed 13/11/15
Business Sheets - these exist with and without SBP
2nd class2nd Large
Booklets: information awaited.
Because I have concentrated on year codes as and when the arrive or are discovered, I have not kept track of whether our supplies have bright or dull phosphor. A later version of the Norvic Security Machin Checklist will have this information when it is finalised.
At this stage I cannot supply specific types for any of the 2015 issues.