I believe 前期底稿 actually means 前期的工作底稿.

工作底稿（Working Paper）是會計師業執行專業工作的真實記錄，包括：審計目的、審計範圍、審計計畫、審計程序、審計結果、審計意見及相關的憑證與文件等等。這是會計師用來證明其遵循專業準則執行審計工作，並作為對於客戶的財務狀況及報表，表達專業意見的唯一根據。因此工作底稿就成為審計人員在實踐領域中進行工作與學習最重要的平台。

閱讀前人或前期的工作底稿絕對是非常好的學習機會，同時非常有利於在實踐領域中執行審計工作，但是由於會計師業對於審計客戶的工作底稿具有保密的職業道德規範，因此除非是參與該審計案件的審計人員，是無法閱覽的。因此如何在不違反職業道德規範下，根據實際工作底稿建立多種樣板，供審計人員研讀與探討，是非常值得進行的。
http://www.cc.ntut.edu.tw/~sylau/clementyang/CPA.htm

Also, Article 43 of Taiwan's Certified Public Accountant Act (會計師法) states:

會計師執行業務所為之簽證，業務事件主管機關有疑問時，得向會計師查
詢，或調閱有關簽證之文件及查核工作底稿，會計師不得拒絕或規避。
Where the competent authority with the relevant jurisdiction has any doubt regarding the attestation made by a CPA in the performance of professional practice, it may inquire of the CPA concerned or request to review any attestation-related documents and audit working papers, and the CPA may not refuse or avoid cooperation with the inquiry or request.



--------------------------------------------------
Note added at 35 mins (2008-11-07 03:57:42 GMT)
--------------------------------------------------

The Chinese version of 會計師法 can be accessed at:
http://db.lawbank.com.tw/FLAW/FLAWDAT0201.asp

The English version of the Certified Public Accountant Act can be accessed at:
http://db.lawbank.com.tw/Eng/FLAW/FLAWDAT01.asp?lsid=FL00725...

--------------------------------------------------
Note added at 39 mins (2008-11-07 04:01:51 GMT)
--------------------------------------------------

Audit working papers are the documents which keeping all audit evidences obtained during financial statements auditing. Audit working paper is to be able to support the audit works done in order, sufficient and assurance audit evidences have been obtained and reasonable assurance audit conclusion can be made in due course.
http://en.wikipedia.org/wiki/Audit_working_papers