Previous earning - Period of earning or salary receive date?

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Salaried employee - Previous earning evidence confusion. Period of earning or salary receive date?

Scenario 1.
1. Period of earning: 01/06/2011 to 30/06/2011.
2. Payment date: 07/08/2011
Question 1:
In order to show the evidence, which one I need to select either Period of earning or payment date?

Scenario 2.
From Immigration Guidance: - 103. We will only include allowances (such as those for accommodation or schooling for an applicant’s children) in the assessment of an applicant’s previous earnings if they are part of an applicant’s remuneration package and are not paid to reimburse the applicant for money he/she has previously spent.

In my case:
Contract start date: 01/July/2011
Contract end date: 30/Dec/2011
Type: Salaried employee.

July Contract started -> reimburse expanses end of every month -> get pay slip -> get bank statement -> after 5 months, in the month of December I came to know I wouldn’t be able to show my gross salary as my previous earning, because I reimbursed expanses. -> So I decided to pay tax for the previous months i.e. from July. -> I made a request to the employer that I am willing to pay all my tax and NI from the month July -> Employer agreed for payment recalculation -> by this way I will get a new pay slips, but bank statement I still need to use the existing.

Conclusion:
I am going to pay all the tax and NI for my gross salaries. In order to show evidence. I was thinking to show my pay slips, bank statement and employer letter explaining the entire gross, net, tax, and NI.

Kindly please advice on this