The notes were a response to a shortage of £1 notes and had been printed in 1963 with non-standard prefixes, 01X and 02X.
Interesting indeed.
Central Bank of Ireland One Pound 1963 01X prefix.

These notes also exist with dark ink date and serial numbers, the mulberry variety.
Not a very good pic on this one, but it does illustrate the difference.
Central Bank of Ireland 1 Pound 11.3.63 01X prefix, Mulberry serial numbers.
