Carryover fouls

[ljudge]

It has always been my understanding that fouls during a TD-scoring play may not carry over to the 3rd quarter. Say, for example, foul was committed during the try at the end of the 2nd quarter. May that be carried over?

Some situations...can someone please set me straight? Assume team A wants to keep the points in all situations and enforce on succeeding play.

Sit 1: A scores a TD-scoring play on the last play of the 1st quarter.

Ruling: Enforce on kickoff. Untimed down

Sit 2: Same as #1 except at end of 2nd quarter

Ruling: Can not carry over to the 3rd quarter.

Sit 3: Successful field goal at the end of the 1st quarter

Ruling: No untimed down. Enforce on 2nd quarter kickoff

Sit 4: Same as #3 except at end of 2nd quarter

Ruling: No untimed down. No enforcement of 3rd quarter kickoff.

And, in all 4 situations what if the foul was unsportsmanlike? Am I correct in assuming these don't have to be assessed on the TRY of the USC happens during a TD-scoring play?