Thanks for the clarification. That kind of third party “mixing and matching” of and additions to datasheets does raise questions about the provenance of the data, although in this case I don’t think that it changes the basic picture.
The attached datasheets are extracted from Philips Electron Tubes Part 4 1972, and so apart from the extraction exercise, have not been tampered with as it were.
Philips Electron Tubes Part 4 197206 EAA91.pdf
Philips Electron Tubes Part 4 197206 EB91.pdf
The EAA91 was still the shorter version, and appears to have still been current in 1972. The EB91 was listed as “maintenance only”, and was referenced back to the EAA91 for detailed data.
More insight into the early 1950s chronology may be had from a couple of Philips valve pocket books.
The first of these is Philips Electronenbuizen Zakboekje of 1953. It listed miniature double diodes as EB41, EB91 and UB41, but not the EAA91. The EB91 was shown as the preferred type for 6.3-volt and 300 mA heater applications, with the UB41 the preferred type for 100 mA heaters:
The second is the 1954 Pocket Book mentioned upthread. This listed miniature double diodes EAA91, EB41, EB91 and UB41 with the EAA91 now shown as the preferred type for 6.3-volt and 300 mA heaters. (By then there was no preferred type shown for 100 mA heaters.)
That puts the change from the EB91 to the EAA91 as the primary miniature double diode as having occurred in the 1953-54 time period.
It still does not answer the question “why”. But the previous suggestion remains a good fit. That is, Philips decided that it needed a miniature double diode that was an exact performance and physical replica of the American/International 6AL5, and not simply a performance match. The Australian market requirement may well have been the prompt for that, and once done it was logical that the EAA91, identical to the 6AL5, was made the preferred type, displacing the EB91 from its short reign in that role in most of the Philips world, with the UK being an exception.
Cheers,