About 12 ships if you fill the last remaining pennants:
2nd Destroyer Division: 166, 160
3rd Destroyer Division: 135, 130
6th Destroyer Division: 158, 159
9th Destroyer Division: 176, 177, 178, 179
10th Destroyer Division: 125, 126, 127, 128
Each Destroyer Division is maxed up to 10 ships of 052X. 10th starts at 119, so it ends at 128 instead of 129.
After you complete the 12, then you start to retire the remaining destroyers, which would have been refitted 051B, 052B, and Pr 956. :
167, 168, 169, 136, 137, 138, 139.
Brings you to 19 ships. If they decided to use 129 anyway, that will be a total of 20 ships.
Type 055 will occupy 109 to 116, with destroyers 112, 113 (type 052) and 115, 116 (type 051C) retired to release their pennants for their replacements.
140 to 149, 180 to 189, 190 to 199, remain reserved if PLAN wants to add three more new destroyer divisions.