The clustering MGF output file will look like:
BEGIN IONS
TITLE=cluster-1;mzspec:PXD004732:01650b_BA5-TUM_first_pool_75_01_01-3xHCD-1h-R2.raw:scan:17555:VLHPLEGAVVIIFK/2
PEPMASS=318.185
CHARGE=2+
SEQUENCE=VLHPLEGAVVIIFK/2
1.5 8.84
5.8 0.75
8.285 1.34
17.4 0.32
97.999 1.1
132.017 445.98
158.996 235.36
169.955 4235.4
175.045 518.94
185.063 336.05
209.069 186.72
260.189 1255.96
268.922 159.25
277.729 3557.77
286.234 510.24
334.264 3129.8
339.303 328.09
346.855 400.5
350.224 199.13
383.827 5392.89
402.894 272.86
411.354 1636.43
417.31 2169.19
420.341 446.95
491.367 214.35
519.401 325.75
521.779 35.4
537.578 32.16
554.307 1514.12
592.429 35.01
600.643 1.7
627.992 6.41
647.458 2.33
667.572 61.7
677.451 3.69
713.578 0.65
761.149 0.54
795.495 0.72
808.411 0.68
839.005 1.06
850.931 1.57
869.944 0.86
879.392 0.61
END IONSThe title of the spectrum in the MGF contains the information about the cluster (cluster-1) and the SCAN Number TITLE=cluster-1;USI-ID, spectrum represent the Consensus spectrum, then the USI will be missing or empty.