Graham,
The 4 digit "Type" number defines a combination of "Country" and/or Broadcast Type i.e. PAL or NTSC and/or power etc.
So, any B&O product could have many type numbers depending on where it is sold etc.
For example an AVANT DVD Mark III has 10 different type numbers from from 8460 to 8469. Type 8463 is sold in the UK whereas Type 8465 is sold in Australia, but all type numbers are AVANT DVD Mark III