Original sentence: Due to the marketing considerations mentioned above, many people mistakenly believe that other networks are Tier 1 (by the generally accepted definition) when they are not.The following 9 networks are the only Tier 1 ISPs, by the generally accepted definition:
Edited sentence: Due to the marketing considerations mentioned above, many people mistakenly believe that other networks are Tier 1 when they are not.The following 9 networks are the only Tier 1 ISPs: