A standardised clause for submitters to a journal should both transfer some copyright to the mazagine (so they can organise publication elsewhere - eg in a 'best of' collection, allow reproduction by other magazines etc) as well as confirming that the submitter holds the copyright in the submitted material - that was the usual situation in academia. This would avoid many future problems - it was the assumption I'd made until I became editor.

As in your case literal copying of a chapter should certainly have resulted in an abject apology by the magazine (I assume a small amateur society one as commercial magazines AFAIK use a transfer of copyright scheme similar to that described above and should also in that case have paid you an author's fee as well as an apology).

One thing should however be pointed out is that the information contained in any copyrighted article is not itself copyrightable - I have seen several cases of family historians being told they cannot use some material as it is 'owned' by another researcher - this is not the case, even lists of names and dates if the format is effectively the only feasible arrangement are not copyrightable. It may be the case that you acquired the information by agreeing to a contract not to publish it (common in industry and known as Non-disclosure agreements)- if you did publish it and someone else then innocently uses this information there is no comeback on the innocent user though the secondary publisher could be held liable for breach of contract.

In many ways the laws on copyright are out of date with respect to the changes that a digital world has wrought - it is based on an old notion that the cost of reproduction was high and thus some control was possible (originally for a much shorter period) by controlling the right to make copies - now this is a nonsense as anyone with access to a CD burner, photocopier or scanner knows, but so far no better scheme has been agreeable to all parties concerned, the producers, the publishers and the consumers. For the vast majority of articles the 70 years copyright law is a nonsense leading to major problems in tracing owners of copyright that they (or their descendants) have no interest in maintaining) - a copyright scheme allowing non-commercial republication (ie. for no more than the proportional cost of the media used) as long as credit is given to the original author and place of publication, would serve very well for 99% of the output of family historians