I first used EFKE Kb 14 (the old DIN name) in 35mm back around 1978 shortly after it was imported into the UK, the claim was LF quality from 35mm negatives. Back then there was almost no emulsion hardening and I added either a hardening stop-bath or some formaldehyde to the developer, yes it was exceptionally fine grain, but too finicky. Later Fotokemica improved the hardening quite significantly.
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Because Adox, and later EFKE Fotokemica, used the DIN method for speed testing there was no revision (doubling) of the film speed, unlike the ASA/BS standard changes of the early 1960s.
Ian