With payroll records from both the acquired entity and the acquirer, the purchase agreement, and documentation showing the employee's service was continuous rather than terminated and rehired.
The payroll changes name; the employment must not break
The one continuous year of full-time employment must be with a qualifying organisation within the three years before the petition. Where an acquisition occurred midway, the record will show one employer name and then another, which invites the question whether employment ended and restarted. Answer it in advance.
Provide payroll registers or pay statements covering the whole period without gaps, the purchase agreement and any assignment of employment contracts, the letter given to employees at the time confirming continuity of service, and confirmation of unchanged benefits or seniority where that applies. If there was a genuine break, say how long it was and where the qualifying year falls as a result, because a short gap may push the required year outside the three-year window. Reconstruct this from records before writing any support letter, since the letter must match what the payroll shows.