Regulation E does not care about your ability to use the VISA Chargeback process to investigate a claim. Reg E 1005.6(b)(3) places liability on customer based on their timeliness of reporting unauthorized activity.
1005.6(b)(3) states that you must first identify the date of the FIRST unauthorized charge. Second, determine the date you provided the statement on which that charge appeared. Third, count forward from that statement date 60 days. The Bank is liable for that period of time between the FIRST charge and 60 days AFTER that statement. Your customer is liable for anything AFTER that 60 day period.
Notice how Reg E counts time forward from the start of the fraud, but VISA counts time backwards for what it allows you to dispute. You may find that Reg E requires that you reimburse a customer for charges further back than 120 days. So the Bank has a decision to make. It cannot offset earlier losses by filing chargebacks on more recent transactions. However, it may be worth filing a chargeback or two on the more recent charges to see if you can obtain enough information to lead you to conclude that all of the charges were actually authorized. Alternatively, you could choose not to investigate and just reimburse the customer for those early charges and skip the chargeback process altogether. Lastly, if PlayStation has a customer service number, you may want to contact them directly to try and learn more about the transactions outside of the chargeback process.
The other component to consider, is that if the customer did not notify you of the fraud within that 60 day timeframe after the delivery of the statement, 1005.11 does not apply which means you do not have to provide provisional credit or complete your investigation in 90 days. This gives you some time to decide how to proceed.