P45 and P60 are different....

Hi, it's been ages since I've been on these forums but I have an urgent problem and really hope someone can help?! I have a client who was made redundant last year and is now setting up as a Ltd co. I am setting up his payroll but am confused as I have different figures on his P45 and P60... His redundancy package was £15k in feb , £15K in Mar 15 and £66k in April. He was of the understanding that the £66k was in the 15-16 tax year and when I completed his SATR I didn't include it as his P60 looked to be his normal salary plus the two £15k amounts.
I now have his P45 from this employer, but the tax code and amounts are different to his P60, it also states his leaving date as 31/1/15 but is dated 4/4/15. The tax code on his P45 is 1204L but his P60 is 935L. There was outstanding tax of £441.40 from 13-14 which was being collected through the 15-16 tax code but he paid this in full in March 2015.
Am I missing something obvious for which I will be embarrassed? Should I enter the details from the P45 in to the new payroll and ask to see all his payslips for 14-15? help....
Thank you in advance!!
Lucy