In the past, it was Library of Congress practice to uniformly romanize the
frequently-used character as ti when it was used as a possessive
particle or adjectival ending, even though it is usually pronounced de.
This was an exceptional practice. (The character can also be pronounced di:
for example, 
is romanized mu di.)
The Wade-Giles syllable ti converts to the pinyin di. When the National Library of Australia converted its bibliographic records to pinyin, records in which the syllable di occurred were manually reviewed, and, in most cases, the converted syllable di was changed to de. However, the Library and the utilities, RLG and OCLC, agreed from the outset that it was not feasible for us to identify the syllable di in hundreds of thousands of converted Chinese authorities and bibliographic records, evaluate each instance, and then manually change the syllable to de where appropriate.
Therefore, the pinyin conversion specifications did not single out the Wade-Giles syllable ti for any sort of special treatment: it is simply being converted from Wade-Giles ti to pinyin di. For example, the machine program converted the romanized title
T'ai-wan jen ti wen hua kuan () to
Taiwan ren di wen hua guan
The new pinyin romanization guidelines direct that Chinese syllables should
be romanized according to the way they are pronounced. Since , when used as
a possessive particle or adjectival ending, is generally pronounced de,
in most instances it should now be romanized as de. For example, the
title above would now be romanized
Taiwan ren de wen hua guan
However, when searching for that title, one should remember that the romanized
form of could be given as either di or de.
When encountering authorities in which was converted to di by machine
program, change the romanization of that syllable to de; then make
the same change to headings and titles on corresponding bibliographic records.
Similarly, when encountering a bibliographic record in which was converted
to di by machine program, change the romanization of that syllable
to de. If the romanized syllable is in a heading, make the same change
to corresponding authority records.
These changes will be carried out on an "as-encountered" basis only, and not as a special cleanup or rectification project.
Library of Congress