I recall hearing that they changed the rules a few years ago and personal and business sign up bonus eligibility no longer separate. I.e. you wouldn’t get Amex business card sign up bonus if you have been an Amex cardholder in the last 18 months.
This is the one area I get a bit annoyed about with Point Hacks - all well and good to tell us about all these great sign up bonuses but nearly all credit card operators now require that you are a new customer and if you have or have had one of their cards you are not eligible!