Welcome to the Q&A Forum

Thank you SO much for raising this question! The Beginner's Guide To SEO is currently being updated and will address exactly this. Google's John Mueller has stated in the past that it's ok to put a link on a client's site back to yours as long as it's rel="nofollow". When I was previously self-employed at Pryde Marketing, and heard Google state this, we instantly changed our client footer "Made by Pryde Marketing" links to rel="nofollow" and almost immediately saw organic improvements. I can't say for certain that changing our client > Pryde links to "nofollow" 100% caused this, but it didn't hurt. My personal opinion is that you can benefit from clients linking back to your site in a credible way (ex. If you built their website) and have a rel="nofollow", you will be fine. If you reverse engineer any of the top web developer's sites, you'll likely see quite a few "built by xyz" linking back to their domains.

Ok, that's good to know. I think for now, I"ll leave them alone, unless there's one that seems really irrelevant. Thanks to both of you for your help.