Overtime and holiday pay employers letter

Hi again, thank you every one for previous advice, Our application for flr m is going in on the basis of meeting the £18600.
my employer has given me the following letter
I can confirm that mrs ----- has been employed by ------- at the above address since 1st July 2014,

mrs ---- earnings for the period 2nd December 2015 to date are £12383.29

Mrs ---- is employed on a permanent contract and works an average of 40.25 hours per week,
Overtime is paid at the rate of time and a quarter, Her current rate of pay is £7.20 per hour,
I can confirm that the address we hold on record for Mrs ----- , is -----, -----. ----- . -----, Should you require any further information please do not hesitate to contact me at the above address,

From these figures it is clear they have only included my basic hourly salary, they have not included holiday pay , or over time, these together add to a further £8500,00. i have all pay slips and am awaiting missing bank statements which will match pay slips.
should the letter state the total gross salary including holiday pay and overtime,
which is the best route to go, My husband said A but still provide 12 months slips to show total paid salary for year , we also have last years tax paper with total earned, i realise that it is not really any good as the tax year ends in April but people do say send it any way, any advice would be greatly appreciated
many thanks
Yan