PDO (Philips DuPont Optical, Blackburn, UK)

UK CD and Laserdisc manufacturing, based in Blackburn, UK from December 1986 until March 1996. Company later transferred to PMDC, Universal M&L, UK. Distronics Blackburn Ltd, Deluxe Global Media Services Blackburn Ltd. and finally EDC Blackburn Ltd before being closed in 2009 and manufacturing transferred to EDC Hanover, Germany.

Origin of the infamous Rotten CDs. These CDs will turn yellow and rot away due to manufacturing faults. https://en.wikipedia.org/wiki/Compact_disc_bronzing

Disc Matrices will show Made in UK or Made in UK by PDO

Discs manufactured here had a sequential numbering system, unique to this plant:
Between 1987 and June 1989 the pattern consisted of 6+2 digits:
XYYYYZ NN (e.g. 134231 01)

where X = 1 (first disc) or 2 (second disc for 2xCD editions) and Z = number of discs in the set
YYYY = sequential manufacturing number,
NN = 01 up to 09 or even higher (potentially the glass master number).

From July 1989 onwards, the system was enhanced to 8+2 digits, with optional symbol presumably identifying the LBR:
XYYYYYYZ NN (e.g. 10133491 01 or 20133491 01 %)

where X = 1 (first disc) or 2 (second disc for 2xCD editions),
YYYYYY = sequential manufacturing number,
NN = 01 to 09, 10, 11, etc. (potentially the glass master number).

The pattern was valid for all discs types (CD, CD-Single, CD-Mini, or CDV).

(Some of these numbering details are from discogs.com)

Example images of a rotten PDO UK CD
https://musicbrainz.org/release/57996834-94cb-4bcd-8925-ebc1baff542f/cover-art