Your Momma Bear either misses the last days of several months, or counts extra days. It also fails to count the LastMonthOfYear. Your Baby Bear is nothing like your Momma Bear, though you seem to be refactoring. Momma counts entire months (look at the variable names, last day of month), Baby does something like "sum the totals from the first five days of Feb-May". These are naming bugs, they aren't irrelevant.
The naming depends on the code. If we're iterating a 3d array and the vars are set directly above, Papa Bear is readable and I wouldn't dick around with it (it might be a convention in the codebase).
// baby bear
for(y=firstY; y<=lastY; y++)
for(m=firstM; m<=lastM; m++)
for(d=firstD; d<=lastD; d++)
sum += getDailyTotals(y,m,d); // line 4
I'm not saying you should choose single variable names, I'm saying they're sometimes ok, and that it's not as simple as "choose names with 4-8 characters".