What's easier and faster to consult than Google?: on this forum hands down that'd be Steve Tall. The depicted Plumb catalogue seems to be a compilation of different 'effective' dates; some Aug 1 1956, Mar 2 1964 and Oct 18 1965. Retailers often received updates to file in their product binders so the different dates isn't surprising. The sheets, some of which are dated Aug 1 56 (at least 2 pages), which also says "-Over a century of quality- since 1856-", describes the new process and states that "all Plumb axes now have the exclusive PERMABOND assembly".The Plumb Catalog with the relevant Price Sheets dated 1964 shows 3 sizes of the National pattern:
3-1/2# (with a range of handle lengths available)
2-1/4# (with 28" handle), called the "National Boys"
1-3/4# (with 16" handle), called the "National Utility Axe"
https://archive.org/stream/PlumbTools1965/Plumb Tools 1965 150 dpi#page/n13/mode/1up
There was some debate on here a while ago (fielded by Operator 1975) who disputed (even convincingly dispelled) claims of all Plumb axes being Permabond hung in the initial years of introduction.
Still unknown, to me anyway, is when the Nationals were discontinued. Are there any Ames era catalogues (1971 to 81) out there for us to peruse?