PENDF head for MF3 MT1 with 99

[roubtsod]

Hi all!

I was looking at NJOY-generated PENDF files (reconr , broadr) and i noticed that NJOY assigns 99 in the head record of MF3 MT1 as follows:
(H-2)
1.002000+3 1.996800+0 0 99 0 0 128 3 1 1
0.000000+0 0.000000+0 0 0 1 359 128 3 1 2
...
(Th-232)
9.023200+4 2.300450+2 0 99 0 09040 3 1 1
0.000000+0 0.000000+0 0 0 1 504339040 3 1 2
...
For other reactions, MF3 MT2, ..., the head records are with zeros, e.g.
(H-2)
1.002000+3 1.996800+0 0 0 0 0 128 3 2 1
0.000000+0 0.000000+0 0 0 1 359 128 3 2 2
...

For File 3, ENDF-6 manual reads:
... The structure of a section is:
[MAT, 3, MT/ ZA, AWR, 0, 0, 0, 0] HEAD
...

My question is: what is the meaning of 99 in the head record of MF3 MT1 (if any)?

And changing this 99 to 0 in the NJOY-generated PENDFs (reconr , broadr), for further processing with NJOY (e.g., groupr or acer): is it safe?

Thank you!

Dan Roubtsov
CNL