Yes, these are a "good find", and nicely played. I see the collective title is "21 Preludios vascos", and "vasco" actually means "Basque".
As Chris points out, they don't sound particularly Spanish. I don't know, though, if there was as much animosity between Basques and Spanish a century ago as there has been in recent decades.
I was intrigued by the fact that the name "Donostia" does not appear on or in the score, which simply calls the composer "P. [for padre] José Antonio de San Sebastián O.M.C.".
So it's Father Joe. Is Antonio his surname or is it a second forename? Who knows. A little detective work reveals that Donostia is the Basque name for the city of San Sebastián. I don't know what OMC stands for, and presume it's to do with his religious order.
The end of #3, though, is not what's in the score. In the next to last measure, the C# octave is only an 8th note, and I think you held it too long even with artistic license.
Well done to spot the discrepancy, but on this occasion I would not be so quick to blame Monica.
The score itself is a mess here; the note values don't add up, whichever way you try to make them fit, and so it's difficult to know how it's meant to be interpreted.
In particular, are the octave C# 8ths meant to be followed immediately by the octave Bs, or should there be an 8th rest first? Both alternatives make sense if you compare similar material earlier in the piece. If you consider the Bs as belonging on the second (quarter note) beat, then Monica has not taken as much licence as you suggest, in terms of lingering on the C#s.
Either way there is an 8th rest missing in the score (either before or after the B octave half notes).
What is the meaning of the printed quarter rest? What specifically does it come in front of?
One possibility is that the 8th rests are omitted after the C# octaves because that voice (the theme) has come to an end and the composer or typesetter did not want to clutter up the score with the 8th plus quarter plus another quarter rests. Instead a new voice appears, namely the octave Bs, and the quarter rest belongs in front of them
Another possibility is that the quarter rest is meant to come in front of the three groups of (RH: 8th plus two 16ths, LH: triplets), but then the bar would have to be a 4/4 bar.
Monica seems to be playing it as a 5/4 bar, with the triplet groups taking up beats 3, 4, and 5), but there seems to be no notational basis on which to justify that.
The simplest explanation which occurs to me is that this bar should really be two bars, the line to be inserted between the octave Bs and the triplet groups, and of course the tied bass chord would need to be duplicated in the second bar.
I had to beat rainer to an observation like this just once!
I think there are some rhythmic inaccuracies in No4. It's to do with the music changing between triplets, 16ths, and 8ths.
Looking at the top of the second page, for example, the first bar just has six triplets, three on each beat. The second bar has 16ths on the first beat and triplets on the second, but it sounds to me like the 16ths are speeded up, with two of them corresponding to the duration of a triplet, thus the bar lasts for 5 triplets. The third bar has basically four 8ths, except that the middle two are coalesced into a quarter. But the first and last 8ths are played at the same speed as triplets (not always), so the quarter comes too early, and the bar also lasts for 5 triplets. This pattern continues.
I really like the tranquilo section at 2:10. A brief episode which is less sad than the title suggests, it's more reminiscent of a lullaby or of pleasant memories. Pity it only lasts 8 bars.
Although Chris is right about No9, this liberty is expressly permitted by the instruction "libre