Pirelli never made any paperweights. They (Pirelli) were owned by George Dunlop and located in London. They distributed Vasart and (possibly) Strathearn paperweights under a marketing arrangement. In 1959 advertisements in trade journals, Pirelli claimed Vasart as a subsidiary although the claim was probably false.
For more information, see the 2015 Annual Bulletin of the Paperweight Collectors Association article by Angela Bowey and Allan Port.