Payroll registers, records of employment, layoff and recall letters and benefit continuation records. Together they show whether the relationship continued through the layoff or ended and restarted.
Reconstruct the last three years from paper, not from memory
The question is whether there is one continuous year of full-time employment within the three years before filing. Start with the payroll registers for the full period and mark every gap. For each gap, find the record of employment, the reason code, any layoff notice and the recall letter, and check whether group insurance or pension contributions continued.
A layoff recorded as a shortage of work with a fixed recall date and continued benefits looks very different from a termination followed by a new hire. If the most recent twelve months contain no gap, the earlier layoffs are largely irrelevant and the file should simply show that clean year. If the last year is broken, the honest options are to wait until a continuous year has accumulated or to consider whether the interruption was genuinely temporary, supported by the documents rather than by assertion.