Yes, Hershey chocolate was one that was rumored in the 60's & 70's, to contain blood because of containing 'lecithin'. I do not recall any other brands (ie: Mars) being boycotted.
Most lethicin is sourced from soy beans but some is derived from animal sources such as egg yolk. Some witnesses thought that animal source meant from the animal's blood. It seems, many JW's didn't bother to research what lecithin is but they were happy to pass-on whatever scandolous rumor they heard.
Other products not for JW consumption were certain brands of deli meat & wieners such as 'Maple Leaf' whereas brands such as 'Schniders' were OK as they were 'Kosher'.
Certain brands of pet food were also suspect as was some household or construction adhesives made from animal sources (ie: horses).
I think many witnesses initiate statements due to paranoia or ignorance as do some in general. Unfortunately, many of those statements perpetuate throughout the JW organization due to who else may have repeated them (ie: a CO, DO etc). If someone of rank within the organization said it, it generally is accepted without question. If the info is coming from one of these prominent sources, of course, rank & file witnesses better accept and comply.
I think that many witnesses are looking for some excitement or importance so rumour and heresay such as 'did you hear '____' deli meat contains blood' seems to be enough excitement to satisfy and often provides the teller with some sense of importance.
Isn't it stange how yesterday's 'truth' that no part of blood was to be used, has now been replaced with the use of blood fractions being a conscience matter. If lethicin had been derived from blood, it would probably have been a very minor fraction at best. To my knowledge, the Bible has not been updated by its Author to make allowances for modern technological advances.
It's also funny (sad) that a rumor circulated almost 40 years ago, still pops into my head when I'm looking at deli meat or wieners in the grocery store.