Form 1095 C & Look Back Period

You're misunderstanding how the look-back measurement method works.  While it's true that employees who were in a limited non-assessment period or otherwise not full-time for all months in the calendar year do not need a 1095-C, that would apply only to new hires.

In other words, a new full-time hire can have a LNAP of the first three calendar months.  A new variable, part-time, or seasonal hire can have an LNAP based on the initial measurement period and initial administrative period of up to 13 months (plus a partial month for a mid-month hire) combined.

But ongoing employees will be in a stability period based on the prior year's standard measurement period.  Their status in 2021 is kept "stable" during the stability period based on the prior standard measurement period.

For ongoing employees, the most common approach for a calendar plan year would look like this:

• Standard Measurement Period: 12 months, ending with a two-month gap before the start of the stability period.
  • Calendar Plan Year Standard Approach: November 1, 2019 – October 31, 2020
• Standard Administrative Period: 2 months, comprising the two-month period between the end of the standard measurement period and the start of the stability period.
  • Calendar Plan Year Standard Approach: November 1, 2020 – December 31, 2020
• Standard Stability Period: 12 months, tracking the employer’s plan year.
  • Calendar Plan Year Standard Approach: January 1, 2021 – December 31, 2021

So even though there's a 12-month measurement period, that would have completed prior to the start of the stability period that applies to determine employees' full-time status in 2021.  Ongoing employees' full-time status for 2021 is determined by the standard measurement period that ran from the end of 2019 to the end of 2020.  Employees who averaged 30 hours per week (i.e., reached 1,560 hours of service) during that period are full-time for the 2021 stability period.

Here's a longer overview: https://www.theabdteam.com/blog/key-decision-points-in-aca-reporting-vendor-setup-questionnaires-part-iii/

Great thanks. This is for a temp staffing firm so 99% of the employees are new hires.