Complex sentence: The lettering, typically describes for which series car the part was originally developed, however there are exceptions with some BSW parts not fitting on the Burns as well as many parts which can be used on either the Burns or Inferno series.
Split into simpler sentences: The lettering, typically describes which series of car the part was originally developed for, however there are exceptions as some BSW parts do not fit on the Burns. However there are also many parts which can be used on either the Burns or Inferno series.