Gilbert Erector Set Guidebook - acghs.orgarranged. A particular set could have had many variations in the same year. If a batch of old parts was found with a different finish than was used in a particular set, they were used anyhow. A 7-14 year old wouldn’t notice or care! The information presented should be used as a guideline, more than the definitive rule.
https://www.acghs.org/wp-content/uploads/2014/02/Gilbert_Erector_Set_Guidebook.pdf