In my day we used to note the new freq on the plog at the relavent position. I still do it but a lot I notice are not and maybe a contibuting factor. If you are given a wrong or useless forward freq change, one is able to go back to the noted freq. Yes I am aware the modern avionics remembers the previous freq but is not full proof. the freqs are written on the chart to but not always correct for the day and your position.
Rec freq, readback, write it down on plog, then change freq then call.
Just my 2 pence worth.
As for 121.5 abuse, it discusts me. One day someone will need to get a word in on that freq, real quick. At the moment they would be lucky to get a word in edge ways.