Making restore disc question.

This may be dumb, but it has me curious. When I bought this laptop it
suggested making a set of restore discs. Said to use recordable DVD's or
CD's. I tried with blank DVD+RW's they would not work, someone said has to
be + 0r - R only. So today I picked up a pack of the +R's was looking for a
5 pack since I just needed 3, glad I had to buy 10. I took 3 and had the
computer format them, the got the same error message I got with the +RW's,
saying they not blank. Finally I got one out of the pack and just put it in
the drive and it worked, so made the 3 recovery discs. Then out of curiosity
I tried putting some stuff on one of the 3 that would not work, they will
let me put info on them and read it. Just curious why after having the
machine format these, it show's they are not blank? Does not matter as I use
external drives to back stuff up anyway so the rest of them will end up in
the "junk drawer" just idle curiosity.
--
Beer is proof that God loves us and wants us to be happy. --Benjamin
Franklin