The most recent rerelease from Sino-Platonic Papers is Dì-yī ge Lādīng zìmǔ de Hànyǔ Pīnyīn Fāng’àn shì zěnyàng chǎnshēng de? (How Was the First Romanized Spelling System for Sinitic Produced? / 第一个拉丁字母的汉语拼音方案是怎样产生的), by YIN Binyong (尹斌庸).
The author should be familiar to regular readers of this site, as he wrote the standard works on Hanyu Pinyin orthography — Chinese Romanization: Pronunciation and Orthography and the Xinhua Pinxie Cidian — as well as Pinyin-to-Chinese Character Computer Conversion Systems and the Realization of Digraphia in China.
The text is in Mandarin in Chinese characters. Here is the introduction.
This is issue no. 50 of Sino-Platonic Papers. It was first published in November 1994.