scratchiness on older lp's

i recently purchased a 1950's set of lp's (ella sings gershwin) and while the records look beautiful for their age, not one visible scratch on any of the 5 records, when they are played there is a lot of scratchiness to them. they have been cleaned in a spin clean. i have only listened to three sides so far. i am wondering if i will be doing any damage to my needle by continuing to listen to this set.
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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.

Surface condition does not necessarily reflect the amount of groove damage that may have occurred.

I've heard records that look great but sound terrible and vice versa.

Beauty is only skin deep.
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If it is a buildup in the grooves your stylus should be digging it out. If your stylus stays clean the record is most likely damaged.