irishpapermoney.com

The Central Bank of Ireland Archive contains various data on the Ploughman notes, including a note of the last £1 notes issued into circulation for each Bank.

Bank of Ireland: 3.7.39, BB09 035000
Hibernian: 5.8.39, HA24 025000
Munster & Leinster: 10.10.39 MA44 028000
National: 2.9.39 NA45 004111
Northern: 7.1.31 EA04 079000
Provincial: 4.11.39 PA24 010000
Royal: 6.9.39 RA28 027000
Ulster: 4.12.39 UA12 049081

Seems odd that the National and Ulster stop on an uneven number, you'd figure they'd issue a full packet at a time.
It might be interesting to see what are the highest number surviving examples, maybe from your survey.

Good idea—I will post the highest numbers seen.

Highest numbers recorded for each Bank.

BB09 031623
HA24 018797
MA44 021573
NA44 099713
EA04 076393
PA24 008190
RA28 023717
UA12 043237

There is an exception for the Munster & Leinster, where some unissued £1 notes dated 6.2.40 were retained by the Central Bank, the highest numbered being 50MA 100000.

EDIT: Munster & Leinster info error corrected.