I got the only book-length study on Gao Bing's Tangshi Pinhui ("Graded Collection of Tang Poetry") - the study is a Ph.D. thesis by Shen Dongcheng, published as a monograph in 2009 . In that book, Gao Bing's date is given as 1350-1423, and the date of the compilation of Tangshi Pinhui is given to be:
- First 90 scrolls named Tangshi Pinhui - from 1384-1393
- Last 10 scrolls named Tangshi Shiyi (published as an appendix to Tangshi Pinhui- from 1393-1398
So, my original assumption of the book being completed by 1398 turned out to be a lucky and correct guess. (I originally made this assumption because it was the last year of Hongwu, where Hongwu is Ming's first emperor's regnal title - my prior research only says the work was compiled during Hongwu.)
There are 3 Prefaces in the standard version of Tangshi Pinhui: Shen Dongcheng gives their dates to be 1394. 1395 and 1401.