1964 Topps Mathews blue line
 

This was in a collection I recently bought. Trying to find how rare (if at all) and whether or not it has any value. I doubt it's worth much but I couldn't find much info to confirm or deny, including in a search here in the forum.

Can anyone help? Maybe there's already a thread here and I missed it?

I don’t know about that specific card - but have seen things like this on other cards in many different sets. The only ones that generate significant premium value is T206 print anomalies and other well known and cataloged errors (like the ‘67 Spezio, etc). This card is probably worth a few bucks more to a print oddball collector but I’m unaware of any significant valuation for it.

Best
Scott

As someone who is an Eddie Mathews collector and a print error collector I would agree with the bold part. There are several oddball/print error collectors on here. In the correct section there is a huge thread full of cards like this one, heck this one might already be listed in that thread.
https://net54baseball.com/showthread.php?t=187722

Awesome! Thank you for pointing me there!!