A few days ago (18th I think?) the devs updated some missions retrospectively to have extra HART and extra foam units required. However, there's no increase in station requirement.
Example, Light Aircraft Crash
Variation A requires 1 HART station. Units needed, 1 ATV, 2 PRV, 2 SRV.
Variation AC requires 1 HART station. Units needed, 2 ATV, 4 PRV, 4 SRV.
This is just one example, a lot of missions were changed with similar effects to this. Could the spawn requirements for the larger one be increased?
Also while I'm here, with this change, comes two variation of some missions, but with differing pay. See: