amazing transformation...how?

Perhaps it was a poor recording. Without knowing what was listened to there is no way to revisit it and confirm what you heard. If you can find any of those original albums give them a spin and see how things sorted out. 

The Dynavector HOMC's are known to be "hot" sounding. I know because I had the 20B in 1977. Looks good on paper but a steely top end. I soon sold it to a friend along with my Empire 698 TT. He liked it, used it for awhile then broke the cantilever. Now I have a secondhand 20A awaiting set up. I hope it will sound smoother than my memories of the 20B. The difference being an aluminum cantilever vs. beryllium - which has been banned because of toxicity.

You may just not have been in a receptive mood the first time! Listening to music can be compared to sex. Things don't always go as planned - until next time!

Hi

Could this be a " mind set' situation?

On your initial listening session you were excited and expecting great things only to be underwhelmed and dissapointed. 

When returning a few months later you were expecting to dissapointed and had set yourself very low expectations only to find the sound not as bad as you remembered.

Our mind and memory can play tricks on us.

Mark

Hello! According to you, the sound was so terrible that it is unlikely that the player itself could have had such an effect. The cartridge may be special if it was in unsatisfactory condition. But if you haven’t touched it all this time, then it’s unlikely to get any better. You didn't mention which phono stage you connected it to or which amplifier. Think, could something have changed in them? Did something happen, for example, to the power supply in the apartment over the past year and a half? How warm was each component including cables? And were there any changes in the room itself that could affect the reflections? Most likely you would have noticed this on the CD, but what if? This is some kind of miracle.

Oh, and you can also assume that everything seemed so high and sharp compared to your previous cartridge and turnable. And after a year and a half, that sound was already forgotten and you looked at the new system with an unbiased eye.

And two more versions. 1. You said that exactly a year and a half has passed, not a year. This means that it was a different season of the year. This means the air humidity could change greatly. Humidity affects the static on records, as well as the speed of sound waves. Many audiophiles notice a strong difference in sound depending on humidity and correct this with humidifiers, since the problem is dry air. 2. Physiological changes. Hearing can be affected by blood pressure. Your hearing can also deteriorate if, for example, you work in a noisy manufacture or listen to music loudly on headphones.

Sorry for the tirade.