Sorry, running around like mad trying to errata four books at once. I finally see what you're saying. I'll check.
Don't be sorry. It's clear, that what you do here is a lot of work for a single person. You should be proud to manage it as well as you do.
Let me sum up how I understand your answers in this thread:
1. A Copperhead round can be fired in a TAG-guided mode, or unguided (just like Homing Arrow IV);
2. If a Copperhead round is set to be unguided it behaves like a regular artillery round (it uses regular artillery to-hit rolls for unguided shells, scatters on a failed roll etc.), except that it always deals only 5 AE damage (regardless of weather it was fired from Thumper, Sniper or a Long Tom) to a hex it which it lands, and to every unit in this hex (except of course units not on the ground - like flying WiGEs, VTOLs etc. - per normal damage rules on p. 182 TO);
3. If a Copperhead round is fired in TAG-guided mode and nothing is TAG-ed by a friendly TAG in an 8 hex radius around the hex it was aimed at on the turn it was supposed to hit, then the round self-destructs dealing no damage to anything;
4. If a Copperhead round is fired in TAG-guided mode, attacks a successfully TAG-ed unit and misses unmodified 4+ to hit roll to hit a successfully TAG-ed unit, it deals 5 AE damage to the TAG-ed unit's hex (except units not on the ground), and every unit in that hex (again - regardless of the kind of artillery it was fired from);
5. If a Copperhead round or a Homing Arrow IV is fired in TAG-guided mode, attacks a successfully TAG-ed hex, you can skip the 4+ to hit roll, because weather that roll succeeds or fails, the round or missile will hit the TAG-ed hex dealing 5 AE damage to the hex, and every unit in it (except units not on the ground). The only way such attack can fail is if you fail to TAG the hex.
Let me know if I understand everything above correctly. This list is also everything that I feel that the rules fail to explain (at least in a way, that isn't open to various player interpretation). I hope it can help you if you decide to make an errata for the rules in question.