> “Monotype fonts which have been specially adapted to these recommendations carry the name affix "1450".”

Even this isn't wholly clear. They should have said:

> “Monotype fonts that have been specially adapted to these recommendations carry the name affix "1450".”

The word “that” defines the subject of the sentence; the word “which” describes the already-defined subject. This is a rule of thumb usually expressed as: “‘that’ defines; ‘which’ describes”.