There are GS1 GTIN "rules" about that (e.g. https://www.gs1.org/1/gtinrules/en/decision-support/decision/3 https://www.gs1.org/1/gtinrules/en/decision-support/d

There are GS1 GTIN "rules" about that (e.g. https://www.gs1.org/1/gtinrules/en/decision-support/decision/3 https://www.gs1.org/1/gtinrules/en/decision-support/decision...), but they are guidelines, and relatively lax ones at that (e.g. gross weight changes of up to 20% are allowed). Anybody in retail more or less knows that manufacturers, and even worse - intermediate sellers - don't bother informing about material changes (e.g. languages on packaging being removed to put some marketing bullshit, opening you to legal consequences). Never mention people reusing GTINs for totally unrelated articles.