The main reason I ballparked 25% is...
I get it. But at the same these are old electronics and just the age, cycles, wear will take out a bunch. Look, 25% is not a crazy guess, but 25% would also mean there would be way more supply out there if that was the case, even with many getting hands on their units. Consider PC-55, even today they are quite a hard find. Consider RC-M90 and with prices dropping recently as demand drops off. Consider how many were sacrificed for donors to make others work.
I think 25 years ago, as we welcomed year 2000, 25% of these things were still out there perhaps. But now...25 years later, age, repairs, restoration donors, age failure of components, iPod, iPhone, streaming, it all applied big pressure and I no longer believe that we're above double digits personally. My gut tells me we're under 10% as a guess.
Of course, this is also variable as 'caution' notes above on the sales data being long gone. Like any product, the top of the line units cost way more, and with that price barrier came an adoption and volume bearer. Fewer made because fewer would sell due to price. And higher complexity often means higher chance of failure, and with that comes higher chance of surrender - e-recycle that thing!
How about we take a guess the volume? We're in the '25% or less' category when it comes to what remains of what was made. Some of us higher in that range, some in the middle, some near the bottom, but 1/4 remains.
If you were guessing volume made...(let's stick with JVC) how many PC-5 were made? How many PC-5? PC-55? How many RC-M90? My guess would be 25,000 to 30,000 maximum of each model including all region variants. Remember, they weren't cheap boomboxes, in a sea of very affordable boomboxes at the time with HUGE selection for consumers. There were plenty of great units out there at 1/2 the price of these JVCs for example. Both 5 and 55 aren't great portable units either if that was your purchase goal. I remember looking at JVC PC-55 in a store in '87 at $299 USD and seeing the Sony FH-211W a few spots over for $399 USD - just $100 more - and that was A LOT more boombox for only $100 USD more. No chance I was choosing the 55 over the 211 I thought to myself, but both were pricey. I ended up buying a Lasonic LPC-30 for $149, it had double deck, EQ, VU meters and DISCO LIGHTS in the detachable speakers. And it was lighter to carry. Do I regret it now? Sure. But back then the $250 USD was like 8 weeks of work at my part time job.