The difference in lifetime between a lipo charged to 4.200V and 4.201V is going to be somewhere between zero and unmeasurable. Unless of course you have some scientific (and I don't mean anecdotal) evidence showing otherwise?
It's also very unlikely that your multimeter can measure to anywhere near that accuracy. Even a well-calibrated top-end Fluke has a basic accuracy of usually +/-0.1%+1 digit so when measuring 4.200V it could read 0.005V out, plus or minus.
You may be rather overthinking this.
Steve