5 June 2017 - Machin 50th Anniversary 1st class PIP Machin stamp from Golden Anniversary MS
The 1st class PIP definitive was originally issued in 2006, when the pricing of mail was changed to size-and-weight, rather than just weight. There were several printings of this by different printers. This new stamp is from the Anniversary MS.
This is not a new stamp in the SG Concise Catalogue level, as only the miniature sheet will be listed. The similar stamp from the PSB may be listed in the Specialised Catalogue.
In the picture, the stamp from the PSB is on the left, and the one from the MS on the right. The whiteness of the head is slightly different.