Part 2 of the history lesson.
I've looked and I can't find my hardcopy of BS 5750 Part 1:1979 (so much for my record retention system). It was the predecessor of 9001.
However, here is the relevant clause from BS 5750 Part 1:1987, ISO 9001 - 1987, EN 29001-1987:
4.9.2 Special processes
These are processes, the results of which cannot be fully verified by subsequent inspection and testing of the product and where, for example, processing deficiencies may become apparent only after the product is in use. Accordingly, continuous monitoring and/or compliance with documented procedures is required to ensure that the specified requirements are met.
It is clear that these are 'uncontrolled' processes (my adjective).The context is controlled processes, the previous 'parent' clause:
4.9. Process control
4.9.1 General
The supplier shall identify and plan the production, and where applicable, installation processes which directly affect quality and shall ensure that these processes are carried out under controlled conditions.
It goes on to list the controlled conditions. However, if the organization (then called the supplier) couldn't operate processes under controlled conditions, there were these 'special processes' - hence clause 4.9.2.
The 1994 edition cleaned up the English and made it slightly more readable. It also put 4.9.1 and 4.9.2 together in one clause. It changed the fundamental context by adding service - 'The supplier shall identify and plan the production, installation and servicing processes...'. It also added 'Note 16 Such processes requiring pre-qualification of their process capability are frequently referred to as special processes..
This has evolved into clause 7.5.2 Validation of processes for production and service provision.
I hope this may shine some light on the topic.