count_npb.py

import os

num_npb = 0
num_files = 0
for root, _, fnames in os.walk('.'):
    for fname in fnames:
        if '.parse' in fname:
            with open(os.path.join(root, fname)) as f:
                s = f.read()
                num_npb += s.count('NPB')
                num_files += 1
                
print('Examined %d files' %num_files)
print('Found %d instances of NPB' %num_npb)

Ran on OntoNotes:

$ python count_npb.py
Examined 13108 files
Found 0 instances of NPB