They have noticeably more give than the other frames, but the vibration isn't bad, because the increased flexibility is not uniform throughout the frame (which would indeed increase the amplitude of frame vibrations), but is limited to the areas where the frame integrity is likely compromised. On one of these racquets (both are early Fansteel, just like the 67 RA unit), several squared string holes in the shoulder region appear partially collapsed (probably the result of one too many string job at the higher end of the original recommended tension range). My guess is that these collapsing holes, or the hidden internal damages reflected by them, are responsible for the low RA readings.
As for the POG 90, I don't have nearly as many of them to conduct a proper statistical analysis, but the ones I have measured averaged 69 RA, with a low of 67 RA, and a high of just over 71 RA. This is certainly more consistent than what I got from the US-made OS units, likely thanks to the completely different production method Kunnan developed to make them, but I would have to measure many more examples to have a similarly meaningful result.
My comment regarding old school racquets being no more consistent in specs than modern ones isn't aimed at any specific make or model; it is the general conclusion I came to after measuring over 1100 racquets from different eras and origins.
There certainly were exceptions, whether due to particularly stringent manufacturing protocol or QC criteria. The 1977 Dunlop "Graphite", for instance, is an exceptionally consistent frame in terms of its flex, even though it came in multiple weights, and the balance can be a bit varied. I have measured 10 of them so far (not as many as the POGs, but these are a lot harder to come by). They produced a mean of 74.4 RA, a median of 74.5 RA, an SD of only 0.9, with a minimum of 73.0, a maximum of 75.7, and a skewness of -0.38. Nothing else I have measured (with a comparable sample size) comes even close.
Just because the present is bad doesn't mean the past is better, even though those of us who are in the declining phase of our lives tend to look back at those good ol' days with more fondness than they perhaps deserve (especially when the present seems to be losing the plot).