What does it mean when it does NOT say Top Rack Only?

I have more plastic stuff to wash in the dishwasher than I used to and
have often run out of space in the top rack, while the bottom rack
might be half empty.

Things used to say Top Rack Only. If it doesn't say that, does it
mean the bottom rack is okay too?

(And btw, has it ever been that much hotter on the bottom rack?)

My water suppply is cold and it has a built-in heater, on my 31-year
old Kenmore/Whirlpool machine.

I'm thinking specifically of

The tall plastic glasses made 20 and 30 years ago with inner and outer
pieces and air in between, that is, thermal plastic glasses and cups.

The plastic ice cube hopper that came with the fridge 30 years ago.

Moderately stiff, not vinyl, plastic ice cube trays, two of which came
with the fridge 30 years ago, and two of which were bought 5 years
ago.

The plastic containers that some Chinese takeout places use this year.
Most still use the folded paper with wire hanger, and some a heavy tin
foil bottom with a clear plastic top, but the two nearest me use high
quality, clearly re-usable, with tight-fitting tops, not as flexible
as tupperware and maybe one step down in cost or quality. (I could go
ask them, but I've switched from one to the other, so I don't want to
go into the first one, and I'm on a non-Chinese takeout diet for a
month)

Nothing on any of these about Top Rack Only.

Thanks for any info.