Do not treat accumulated part-time service across several years as the required continuous full-time year. Have the actual employment arrangement assessed.
Distinguish simultaneous affiliated work
The FAM recognizes full-time services divided among affiliated companies when the aggregate meets full-time work. That is different from averaging unrelated part-time history. The qualifying relationships, duties and relevant period still need evidence.
Two different parties get this wrong in two different ways, so separate them. An applicant adding up years of effort tends to reason from total hours worked. A petitioner drafting a support letter tends to reason from what would be convenient to state.
Neither substitutes for the assessment the rules require. Set out instead what each employer can actually attest to: the dates, the contracted hours, the duties, and the corporate relationship between the entities during that period. The distinction that matters is between services performed simultaneously for affiliated companies, which the FAM recognizes where the aggregate amounts to full-time work, and part-time stints for unrelated employers accumulated across several years, which do not become a continuous year by addition.
Ask counsel to say which of the two the history actually shows before the petitioner commits to a characterisation in writing. Where the answer is genuinely unclear, the honest position is that the arrangement requires assessment, and an officer can weigh that more readily than a confident total the records do not support.