Prospecting in Initros only gives me 3 missions and does not list the last one. A guildmate of mine had tried before and encountered the same problem. Logging did not help nor did switching stations.

IIRC, not all systems have exactly 4 prospecting missions. Some have more, some have less.

Just do them as long as they are available. The total will be 120 anyway.

There are only 3 prospecting missions in Initros.
There are a few others that have 3. Latos only has 2.

Well thank you for confirming. ;)

next time I'll ignore the math