Yes, No.13 did not prove to be lucky for this bank. Although the collapse of the bank caused much hardship at the time, it provided a significant hoard of banknotes for future collectors
Bank post bills were issued by many banks in Ireland in the early 1800’s and became a significant element of circulating currency. Bank Post Bills were designed to transmit money through the post and were payable after a specified amount of time for security reasons. The design of the Ffrench’s Bank Post Bills is very similar to those of their banknotes and as such they are highly collectable.
As for the 30 shillings notes, three types of £3 Post Bill have been observed for Ffrench’s Bank Dublin, examples attached. The early type appears to be quite scarce.