Need detailed explanation on these

Issue 1 Our Subsidiary company often sells inventory to the Parent company at a profit. I do not understand why we sometimes reduce the inventory account but at other times we credit and reduce Cost of Goods sold account. What is the reason for both? Please discuss using specific worksheet entries or account names in your explanation, including tax effects. Issue 2 If our Subsidiary company sells inventory to the Parent company in the prior year, can I assume the worksheet adjustments are the same as in Issue 1 above? Explain any differences required in the entries for prior year compared to current year. Please discuss using specific worksheet entries or account names in your explanation, including tax effects. Issue 3 If our Parent company sells inventory during the current year to the Subsidiary company and it sells 100% of this inventory to an external party by financial year end (30 June), am I correct in saying we do not need to make an entry for this intra-group transaction? Please discuss using specific worksheet entries or account names in your explanation