Yes, parasites can also have a huge impact on the amount of nutrition a snake actually gets to use from their meals. This is right in line with all the other information
you gave about his life before you got him...it makes total sense that his scales seem "weak"...lets hope that time & good care with you will allow his improvement,
even though it will probably be very gradual. A re-check of his stool for parasites might be helpful, just for peace of mind. I think it speaks very well of you that you
noticed this issue...many others would not have.