Ok
Best we assume he was not at Malta, this would explain why there was no interaction with him.
One possibility would be he was lost in a fary Regio and needed some time to find the way out.
And then he had to find the caravan.
Or he was sent out in a secret mission so nobody knows where he was and maybe he will bring some news when he arrives.
Or: He was in the twilight for a longer period of time. This is a bit unusual at his age and warping score, but possible.
If you have any preference I can write a short story as proposal.
He could have been scouting sites elsewhere for the caravan to settle...
Do you mean he left Malta shortly after Jarcovius entered Twilight? (Maybe summer 1219 one season later to find some place for the caravan.)
Or should he had left in Spring 1220?
Anywhere in that range works, you will end up getting area knowledge at 7 pts/season for wherever it is he went exploring for spring and summer 1220
Since spring 1220 Frederic was searching the area around Lyon for a place the caravan could settle.
Now in fall 1220 he is coming back to Malta. His trip was not successful.
In fact he thinks it would have been wise not to leave the caravan at all. But his sodales Marco of Bonisagus who was a friend of Fredeics master Pitivo had convinced him to join him on his search.
Now Marco is sitting in a nice lab in Castra Solis “giving his old bones the convenience they need”.
Torros himself alone would never had managed it to find a space for the caravan. Also he was never really convinced it should be searched in the Provencal tribunal.
He only had joined the small group around Marco because he felt they needed his protection. As soon as they arrived at the castle Castra Solis Marco was not interested in searching for a new place suitable for the caravan anymore.
For a short time Frederic enjoyed the presence of so much other Flabeaus. But soon he felt the duty to find an area the caravan could settle. So he started to search some sites in the provincial Tribunal.
But his arts Intellego and Vim are "…ähm" not really good. Additionally he started to miss his home (The caravan).
Finally he headed back to Malta accompanied only by his loyal shield grog Gustav.
Go ahead and bring Fredrick in in the new arrival thread, since that is still at the covenant. He can at least make a cameo there...
Edited the "Swift as the Swallow"speed to 45 mph 
How much Vis per year is my personal source producing?
per previous ruling, PVS produces 4 vis per year.
Over the last 17 years Frederic´s Personal vis source should have provided him with 17 * 4 = 68 pawns of corpus vis.
He used 10 pawns on his longevity Ritual. I assume he would have used some as a payment for knowledge.
How much is left over?
Payment for knowledge balances with other presumed sources of income- you have 58 corpus vis.