Use employment agreements, employer confirmations, payroll and relevant tax records, supported by travel information and dated descriptions of duties. The evidence should agree on who employed the person, when, where and in what capacity.
Explain discrepancies directly
A salary deposit alone may not identify the legal employer or work location. Where records use a trading name or group payroll company, document the connection. Explain missing periods and retrospective summaries rather than presenting an incomplete sequence as continuous.
Keep proof of specialised knowledge alongside, but distinct from, the employment-date evidence. Assemble the records that fix dates independently of anyone's recollection: employment agreements and any variations, payroll records covering the whole period, tax filings, and benefit or pension records that show continuous enrolment. Add whatever evidences the work itself during that time — duty descriptions in force then, appraisals, project records, correspondence.
Then explain the discrepancies directly rather than hoping they pass. A start date differing between the contract and the payroll system, a gap where an employee moved between group entities, a period of leave, or a name change following a corporate reorganization are all ordinary and all need a sentence. Where the employer's own records disagree with one another, resolve which is correct and say so, since an unexplained conflict in the employer's documents is harder to overcome than an acknowledged one.