It and the other 5400 series scopes include on-screen readout which operates with 5400 series and other non-N 5000 series plugins.
The 5443/D44 labeling does not appear in any annual catalog, but clearly existed as indicated by photos and the manual. The 1975 catalog lists 5000-series scopes with mainframe/display nomenclature. The integrated 5xxx nomenclature and the 5444 scope appear in the 1976 catalog. The 5443 manual is dated March 1975. It appears that Tek shipped early units labeled 5443/D44 between printing the 1975 catalog and changing the 5000 series model numbering which happened before printing the 1976 catalog. The source of the 5443/D44 catalog image on this page would shed light.