You’re welcome.
Yes, you do carry a balance from one round to the next. Let’s use the 1st and 2nd rounds as an example. First you determine your “Unspent” income by subtracting any IPCs used to repair any Industrial Complexes and IPCs used to purchasing units. After you have conducted all combat moves in the game, collect your IPCs and enter it into the appropriate row; this number will be similar to the Round 1 starting IPCs, but less (more) any lost (gained) territories. Finally, add this “Collect IPC” value to your “Unspent” value and carry it to over to the next round. Enter this totaled value into the “Round X IPCs” row and that’s what you have to spend the next round.
I hope this helps, sorry if it’s a little verbose.
Honestly, the sheet is a little overkill in the 1942 version, but in more complex versions like Pacific 1940, where you’re collecting IPCs from National Objectives and reducing IPCs from convoy disruptions, it’s a nice way of keeping track of everything.