My approach is vaguely similar; I tag everything I learn with how mutable is, and periodically I re-examine those that are mutable to see if they’re still true. The more mutable the thing, the more often it’s re-examined. So, that „wegen“ takes the genitive in German, that Robert Clive established British India (and thus can be used as an example of the top of the social pyramid in England at the end of his life, despite starting as a clerk), that Stalin was Georgian, these are all essentially immutable and do not need to be re-examined once learned. Relatedly, the need to remember where I learned it from mostly disappears; you can say “look at the standard references.

On the other hand, that CPAN’s support for random parts of the MIME specification is patchy, that Solaris is available for free for i386, and especially more domain-specific things--say, the vm sysctl calls to make NetBSD behave like a desktop machine (http://mail-index.netbsd.org/current-users/2003/12/16/0001.html)--tend to be much more mutable; and it’s in _these_ cases that where the thing was learned matters significantly and must be retained.

And something deduced from two or more of something else has the mutability of the least mutable “something else,” with the corresponding necessity to retain where it came from. This whole approach does have the limitation that your judgement of what’s immutable has to be good; for example, I learned that certain programming techniques in C were immutably good, from first principles, and then the processor people went and invalidated energetically the given that all of RAM was ~equally expensive to address, so lots of those programming techniques needed to be re-addressed.