Man, look at the number of critical issues that should be taken care on priority!
I did say it was a small one, heh. I know that there are plenty of more urgent things to consider and don't want to detract from any of that.
How hard it is to calculate the Default Merits - Earned Merits? You literally just have to know the default numbers for 5 ranks.
But you also need to know what rank the user was when the system was introduced. That might be simple enough to do now in some cases (keeping in mind that some have already ranked up, so it's not always obvious), but in future, it's not going to be easy at all. Again, using the OP as an example, when hilariousetc does rank up to Legendary, some people might assume they started with 1000 and only earned 80 merits. It's not representative of their phenomenal efforts here.