The void days sound correct to me. Note that these are all half-days, not whole days.
If you had been renewing each month, I don't know why they didn't give you the discount for 5th May back when you renewed in June, or if you renewed before the figures were out in June, in July, but glad that they got it right this time and gave you your overdue discount. Sometimes mistakes are made. The ticket office clerk does not have discretion on the award of void days. These are contractual obligations on the TOC's side. They must be paid/discounted against renewals if declared.
The only other void day in the last 12 months for your journey is for half a day on 8th January.
Season ticket holders all have records in the company's database. Not sure how long they hold them for, but at least I would imagine for a couple of periods in the case of monthly holders, but it is possible that records are kept for a few years in case of audits and challenges from the customer.