999999 Puzzle

Some research has thrown up some questions regarding two Machin faststamps with this office code that appeared on e-bay during June 2013. One item had the session number 121 and the other 157. However the former had a rather curious service mark. It claimed to be 1st Class up to 20g which does not exist while the second is 1st Class up to 100g. Receipts for neither do not appear to exist.

The e-bay lisiting gave the later item's location before sale as Rhondda in Wales but the ident for the seller is listed by e-bay as being from Devon.

The suggestion was that the source of these items was the Birmingham Office but given that the session numbers are so low (121 and 157) and a report from 7 July 2013 puts the lowest session number for any of the kiosks as 12473, it is highly unlikely that these items originated from this office.

Why was it assumed that Birmingham was the source? The seller assumed that since the kiosk ident was 9 then it could only be from Birmingham. In 2012, the 000000 ident was genuinely reported at William IV Street/Trafalgar Square and at Archway post offices in London.

I would welcome more data on these items and if there are others like them.