We wanted to add an R44 to our 135 certificate early this year, and it was just past it's 12 year anniversary. The MR and TR blades were changed since they calendar out at 12 years. The owner of the ship had NOT done the Robinson 12 year "recommended" overhauls and inspections on all the components.
Our FSDO said NO. They said that under Part 135, All of the manufacturers recommended maintenance must be complied with. All service bulletins, all inspections, all overhauls. Even if not mandated by the airworthiness limitations section of the MM. ALL of it.
Your FSDO may have a different answer, but in SO13 the answer is as above.