scratchiness on older lp's

Some folks used a 'horrible' system to 'damp clean' records.
A record brush with fiber nape, and a liquid were popular in the 60's and 70's.
The problem was the fiber and liquid just drove the dirt into the grooves and the combination after a few uses would turn into a hardened noisy horror.

My suggestion is allow the LPs the soak much longer.
Cover the grooves on one side with cleaning fluid with the Lp flat. Let it sit (where the fluid will not evaporate off) for half an hour. THEN reclean in the spin clean. repeat for other side.
Yes it will take longer, but hopefully the grunge locked in the grooves will be removed.

And yes it is bad for your stylus. If i own records with serious noise like that and cannot get them clean, i toss them into the trash.

Wondering how I could accomplish this without soaking the label as well

I have had the same issues with some older classical releases and I just kept cleaning and eventually they got better. I would try what Liz suggests also you might want to try an enzymatic cleaner.

Chuck