it has been discussed over and over and over and over and over again.
it has been discussed in agonizing, excrutiating detail.
original work is copyrightable.
a unique design is copyrightable.
derivatives (taking somebody else's design and changing it) are not copyrightable because they are not original. they are based on somebody else's work.
taking a block from the public domain and changing it a little does not make it copyrightable. again ... not wholly original.
the instructions in a pattern are always protected by copyright.
if the design is based on something in the public domain, it is not.
all you have to do is go to the government website and read the information there. it isn't complicated.
the discussions are made complicated by people who find the law inconvenient. they seek desperately for loopholes and obfuscation so they can rationalize and justify breaking the law.
if it's your idea; if it doesn't exist anywhere else; if it's truly unique and original you can protect it.
if you didn't design it; if you didn't write it yourself, then it isn't yours. make sure your copy is obtained legally. don't make and share copies of it.
it really is that simple.