if you, the writer, holds the copyright on the work, you can do what you want with it... i think you're confusing 'copyright' with 'first serial rights' and such... if you have a piece published in a magazine, for instance, the magazine usually buys only the 'first serial rights'... meaning you can do whatever you want with the piece after it appears in their publication... you can sell it again as a reprint or have it included in any collection of your work as you wish...
it
is s.o.p. to mention in the info pages of a subsequent book, where the various works were first published, but that's not really a total 'copyright' issue... it's just citing prior publication... the place that published it first did not acquire the 'copyright' they only bought and paid for the right to publish the piece first [or second, or whatever]...
there are a variety of 'first' rights, including 'first north american' and others, in addition to 'first serial'...
go here to learn all about the various permutations as well as all the rules and regs governing copyright in the us:
www.copyright.gov
finally, you don't really 'copyright' your work... in the us it's all automatically copyrighted the moment it's completed in any tangible form and you put your name on it... all one does after that is to 'register' the already existing copyright... that's usually done with the library of congress [above link]... and it's not usually done by the writer, but by the publisher, if /when the work takes book form... to register every poem and article would be totally unnecessary and very costly...
hope this helps...
love and hugs, maia
