If you still have the original number (or one tag is still in) you have to replace with the original tag, red tags is only for animals you don't know the flock and/or individual number. I don't know if red tags are now EID too, didn't have to replace any of mine yet (I have not bought in any lambs yet and my own are not yet 6 months, so not yet tagged). I would try and red-tag the breeding stock (if you don't have all the numbers anymore), and give the fat stock the numbers they came with, makes it easier at the market/abattoir.
If you own two fields I cannot understand why you would have two CPH numbers, but it may be a blessing in disguise! You can juggle your standstill quite easily if you have two numbers to send in! (We have 13 days standstill here in SCotland, and moving the sheep between my fields (the rented one has a different CPH) has been a godsend this summer, otherwise I could not have been able to take my goats to some of the shows I wanted to!
My goat kids still have their EID Shearwell tags in, although as they insist on putting their heads through the netting to get at (exactly the same) clover on the other side of the fence I am not sure how much longer they will remian inside. One seems to be a bit infected and weeping... My sheep will have the same tags in about amonths time...