Handwavium. He may have simply hired someone to cast it for him.
That may even be how he met mprogue's magus. Note that a low-level version is fine with me. Is it for the rest of the troupe?
Since my magus will be good at Muto, he may easily know Wizard's Vigil.
l would want to reiterate that tablets for Aegis and Vigil is a thing that is nice to provide as a bonus to such covenant from a position "l want other magi here and l want them see that l had prepared as much as l could in advance so they are less cautious about this endeavor".
Also, they aren't actually costly, so they could be easily afforded.
Agreed. Casting tablets are an option.
Although casting a ritual spell from a casting tablet is very risky. If you roll a 0, you have 9 botch dice for a level 20 ritual.
I know some groups want the highest possible Aegis every year regardless of cost...and others are willing to completely skip it and take their chances unless they suspect a problem. I fall somewhere in the middle.
Might it be a good idea to have a 30-40 tablet for emergencies...but fall back on the discounted 20 for yearly casting?
I generally believe sticking to a 20 is totally acceptable as I think that provides a big enough benefit, especially given our earlier discussed power level.
I was thinking having someone know it and having those casting tablets would be really handy because we could also have stories happen where our Aegis caster is indisposed, so a backup option would be nice.
If we don't want casting tablets, then we should have some lab texts for them at least.
I'm fine with a weaker one. Only spending 2 pawns a year would be nice. I personally have a tendency toward Mastering it with Rebuttal, one of the very few cases I've found that work really nicely with Rebuttal. If you've got Mastery 3 with Rebuttal, Adaptive Casting, and Penetration you can pick up new versions to use well, it works against spells nearly as though it's 2 magnitudes higher, and you get the important penetration boost. But that's just what I do if I'm developing the spell; I'm really not picky at all.
I've wondered about this; how do you practice a ritual spell enough to get mastery? Can you practice without spending vis?
Also, anyone have any thoughts on my question re book prices above?
l guess, you can't really practice it, so you have to read books on it's mastery.
Found it: HoH:TL p.76. It says you can practice Fenicil's rituals like Hermetic rituals and this requires no vis and has no risk:
Like Hermetic rituals, mastery Ability can be gained and developed via practice. The magus practices parts of the ritual, becomes familiarized with the details and contemplates the subtleties. This process requires no vis or risk.
Arthur had pointed out that with our 50 BP those are things that we'll pick up between apprenticeship and arriving, so some books could have been potentially purchased, for example.
My point is, for instance, a L20Q11 book;
according to Cov page 95, should cost 20 pawns of vis (4 BP)
according to the BP table on pg 5 should cost 31 BP
All the books have this difference, a "typical" price in vis much lower than the equivalent cost in BP.
IMO, that is partly because the "cost" of acquiring a book is more than just the vis itself. The time and efforts spent locating the desired book (finding a willing source for the copy) and then arranging for the copy to be made and delivered (several seasons of delay) are all included in the BP cost.
When you acquire it during play, then you need to do the legwork and wait for the copy to be ready before you can study it.
Right. That's why I'd pointed out the bible further up, which could cost 1 lb (0.1 BP) of silver or 50 BP as an extreme example. But it's far more egregious with mundane stuff than with magical or Hermetic stuff, because the mundane stuff is generally available if you're willing to wait a little bit, much of it commonly available in certain schools.
Ok, here's a 300 bp library, with some random selection of Arts, Level and Quality:
It's not perfect, but I think it gives everyone a core to build around when they can decide how to spend their individual build points.
Coming next are some lab texts
How much vis does a personal vis source grant after apprenticeship 
?
6 pawns per year for a Form
3 pawns per year for a Technique
A few basic lab texts for spells:
Casting Tablets:
Total 50 bp
For specialists already at the covenant, I was thinking that the following would make sense:
One additional possibility would be a glass-blower - maybe Leonardus was fond of stained glass windows and found someone to move to the valley.
I initially thought to add a blacksmith as well, but that may not be essential. The covenant can get its iron items from the other parts of the valley, including Laimunt itself.
My maga is likely to be making clear glass (experimental philosophy, but relatively trivial), so doing glassblowing via Rego craft magic. (She thinks the standard Verditius aversion to craft magic is the same sort of silliness like universities not teaching medicine to women.)
Something else to consider is if we'll have any companions. If not, these roles are more essential. But we might well have someone interested in a blacksmith companion or glassblower companion or similar doing Touched by Realm, for example, if we have companions.
Indeed, companions might take up one or more of the specialist roles.
If necessary, I can replace the glass-blower with another specialist, or have him die some time before play begins. It would just make sense that one may have been present when the covenant was slowly being built, if the image of many of the covenant's windows being glass was appealing to more than just me.
If a companion would replace one of the specialist, he can eithe be already there when the magi arrive, or come as a replacement for a recently deceased specialist.
If that happens, I'll simply reallocate the build points to something else. So don't take any of the suggestions as cast in stone.