63 dB re: 50 mW / 4 ohms (or 316-ish µV) is
knot grate. That would have been a rather average receiver back in 1981-ish. You have to try pretty hard to even make a power amplifier that's as bad as this - more often than not they're around 20 dB better. Ground loop in the measurement setup, perhaps?
That's more along the lines of what I'd expect, ref. to full power.
That, too, is rather more like it should be.
"The nice thing about standards is that you have so many to choose from; furthermore, if you do not like any of them, you can just wait for next year's model."- generally attributed to Andrew S. Tanenbaum (also see xkcd #927)
Seriously though, if you read old German reviews you'll find 50 mW / 4 ohm SNR (weighted and unweighted). 1 W / 8 ohm is more of an Anglosphere thing.
In case of a typical power amp, its noise performance tends to be entirely described by full power SNR and gain, IOW you can easily do the math on its expected output noise floor. That is not so much the case when preceding volume controls are involved (since the source impedance presented by a pot changes over its range, ranging between ~0 and Rpot/4), particularly multistage ones (typical modern-day PGAs, or 4-gang volume pots). Hence why testing with the volume turned down is a thing when testing integrated amps.