Re-read what I said.
Yes, reverse/passive DCC works backwards from normal. However, this is not the norm for people sending files. Usually, you do not need to forward any ports to download.
Resuming isn't the same as passive DCC. Yes, it's similar, but it isn't the same. The problem comes not from ports being open or closed on either end. The problem comes from the NAT configuration of the sender's
router. Basically what happens is that the port chosen gets "changed" by the NAT in the router, so that it gets confused because the port that the downloader's mIRC expects and the port that the router tells the sender's mIRC to use don't match. You can search for NAT and resuming on the forum and you'll find more information and better explanations of it than this. However, this is the basic issue. The sender can choose to disable NAT if the router allows that, or possible adjust the router's configuration to not use NAT with IRC (again, if the router allows that). Some routers can be set up to handle resuming, some can't. Others don't have issues with NAT and resume fine without going through hoops. Again, this is on the sender's end, not the downloader's and it isn't because of what port(s) are forwarded.