It appears solid in your pictures, but, those stick on tiles appear to have had water get under them at some time, by the looks of them.

I agree the sub-floor looks fine. But I am concerned that you are breaking up tiles that could be asbestos-containing. Do you know when those tiles were installed?

I’m not sure when they were installed. I have been in the house for 11 years. Built the in 1960.

Your most recent picture just appears to be some staining at the seams of the tile, probably from water. It's still sound.

FYI: asbestos was widely used in the manufacture of such tiles until close to 1980. Not all tiles, but enough that you should consider having these tested. You might be able to get them removed whole with the use of an iron and a wide putty knife or joint compound knife.

Jab it with a screwdriver. If, it goes through, you know it's rotted.

No rot visible. Would be more likely to find rot under the sink, behind/ under the refrigerator.

I agree with Kudzu on removing the tile. Use a scrap of cotton bedsheet or other cotton material between the tile and a warm clothes iron and a wide bladed putty/ drywall knife to lift the tile. The tile should come up mostly in one piece w/ minimal exposure to any potential asbestos fibers.

The SMELL is telling me something is rotten. Pull it all up. Subfloor + tile all in one go. You need to remove all the items in the room to get a better idea of what is going on.

Asbestos was manufacturer (in VCT like yours) until 1982. It was then 'grandfathered' (retailers could sell of the MILLIONS of square feet produced and sitting in warehouses) until the mid-late 1980's. Just be aware that a house in your age range is a Pandora's Box of fun and excitement (no...not the Pandora's box in malls, the real one that was written about in 7th Century BCE as a box of endless complications).

Go with your nose. It is the most ancient part of the animal brain. It is designed to detect danger. It is the first/last warning signal before you put something dangerous in your mouth (or before you drink from a stagnant pool of water....).

Just sayin'. The nose knows. Don't ignore it.

Old vct glue mixed with a bit of muck has a distinctive chemically smell, rot is more of an earthy loamy smell.

It is kind of an earthy smell.... we may have to replace a 2x2 area.

If I were to guess from the translucency (not creamy colored) and lack of any trowel marks, it looks like they used a pressure sensitive glue and rolled it on to hold the VCT. The "wetness" look is not mold or water.

3onthetree- I was thinking that it was probably just some peel and stick tile and we're seeing the residue

Could be, those look like Armstrong pattern VCT to me

Good thing everybody agrees no rotting problem though (from an internet pic LOL)

Looks like peel and stick to me too.

Well, one never knows. By looking at the tile, there has been a moisture issue, so could be that there will be places, that are rotted. No way to know for sure, until its all removed.