LJ,
I'm sure you're a pretty clever guy, so you work it out....
AN/AQS-970/971 sonobuoy processor (Canada) - Jane's Avionics
The AQS 970, as fitted to the MRA4, is capable of monitoring 64 sonobuoys at once. Given that fact, do you really think the aircraft was only expected to drop a maximum of 99 in a single sortie?