If your code is outliving your source control system you got bigger problems than whatever is in your comments. I can confidently say that in 25 years in this industry this isn't something I've encountered. So probably sufficiently low enough probability to safely ignore.
>Moreover, what's the harm? It's more information, not less.
Too much information is every bit as bad as too little.
I've been in the industry less than half that time and it's happened to me. blame will tell you the last person/commit to touch that line of code. To find out when it was originally written, I may have to (in some cases) manually binary search the history of the file.
All in all it has a negligible impact on the readability of the code. It's mostly aesthetic for me. It's ugly and only solves far fetched problems.
Do you scratch your name and SSN into the side of your car? What if your title blows away in the wind on the same day that city hall burns down destroying all ownership records?
(I'm embarrassed I didn't think of it before)
Also, if you're using GitHub, their Blame view also a button that looks like a stack of rectangles between the commit information and the code. Clicking that will essentially do the same thing command-line git operation above.
This lets you quickly traverse through the history of a file. Another good tool for digging into the history is the -S flag to "git log", which finds commits that added or removed a certain string (there's -G that searches for a regex, too).
You've never been at a company that finds it needs to upgrade from $old_version_control_sytem to $newer_version_control_system?
Because I've never seen that done as a big-bang rollout, it's always been "oh that code lives in the new system now, and we only kept 6 months of history"
Even just having an architect manually move folders around in the version control system has broken the history.
I've done this maybe a dozen times. Its always been big bang and I've never lost any history I didn't choose to lose. In fact I just did this last week for a 10 year old project that moved from SVN to GIT.
If you work somewhere where someone tells you this isn't possible consider finding a new job or alternatively become their new source control lord with your new found powers. Moving things between SCM systems is about the easiest thing you can do. Its all sequentially structured and verifiable. The tools just work everytime.