Yes, ant that's why National Institute of Justice lists toothbrushes as a good source of DNA in case the individual from which the sample is needed, is not available.
http://nij.gov/topics/forensics/evidence/dna/basics/Pages/types-of-samples.aspx
There would be a plethora of skin cells on the panties, also a bit of feces and urine and vaginal secretions might be there, all of it contains DNA. And, as far as I remember, police did not take away all the Maddie's clothes and did not obligate McCanns to make a laundry.
A sample containing so small amount of DNA it needs amplification is far from ideal. As for clarity, panties or towel used by Maddie also would contain only her DNA. And please, don't tell me they shared also their underwear and towels.
Still it begs the question why Gerald McCann had to go to the UK to retrieve the pillowcase. Maddie somehow drooled while asleep only at home? Or someone wanted to delay things maybe? And why to give such a weak sample? McCanns are educated people and doctors, they know very well where to find a good amount of DNA.
The reference sample was not amplified.
Why would the mccanns preserve dirty pants for months, and why would they chose them over her pillow.
The pillowcases she used in 5a belonged to the odeon club not the mccanns,therefore they would not be in possession of it months later.
Children on holiday share toothbrushes and again it was months later so why choose a toothbrush over a bigger patch of saliva.
Why is it an issue that her pillowcase was used anyway. Its her DNA unless there is a second mccann daughter missing.