I've owned volumes 1 and 2 for a few years, so unless newer pressings
have been revised, the following should still apply. All tracks in
volume 1 match (by ear) to either Dubravka Tomsic (various budget
labels; my copy is Sonia Classic CD 74537) or Balázs Szokolay (Naxos
8.550252, a 1989 release not part of their ongoing complete series).
Here's the rundown (the Tomsic disc uses Longo numbers):

"Hatto" track 1: K. 162 = Tomsic (L. 21)
Track 2: K. 198 = Szokolay
Track 3: K. 380 = Szokolay
Track 4: K. 87 = Szokolay
Track 5: K. 259 = Tomsic (L. 103)
Track 6: K. 159 = Tomsic (L. 104)
Track 7: K. 466 = Szokolay
Track 8: K. 481 = Szokolay
Track 9: K. 135 = Szokolay
Track 10: K. 146 = Tomsic (L. 349)
Track 11: K. 11 = Tomsic (L. 352)
Track 12: K. 1 = Tomsic (L. 366)
Track 13: K. 19 = Tomsic (L. 383)
Track 14: K. 14 = Tomsic (L. 387)
Track 15: K. 39 = Tomsic (L. 391)
Track 16: K. 551 = Tomsic (L. 396)
Track 17: K. 9 = Tomsic (L. 413)
Track 18: K. 141 = Szokolay

Stated timings are identical to the originals or nearly so, so there
doesn't appear to be any significant time-manipulation. In most cases
I could identify unique (or most likely unique) elements like
fingerslips, a particular pattern of accents or ornaments, or (in one
case) an audible edit, all of which matched to the second. Sometimes I
had to rely on less specific factors like phrasing and dynamics, but
am still confident about the matches-though would be interested to
know if anyone else who's able to make comparisons hears anything
different.

In a few cases, the perpetrator(s) could have copied the same sonata
from either disc, so their choices are perhaps revealing. For example,
Szokolay's K. 146 (Allegretto in some editions) is considerably more
animated (2:39 with repeats) than Tomsic's (3:26 with repeats) and
would not have sounded out of place here, but it was Tomsic's
moderately-paced version that was used. On the other hand, for K. 466
(Andante moderato), Szokolay's (4:42, second repeat omitted) was
chosen over Tomsic's (8:42, both repeats), even though the latter
seems to me more atmospheric and evocative. The K. 159s (Allegro) have
nearly identical timings (2:10 vs 2:09), and here Szokolay seems a
little more interesting: he adds a slight ritard in the first section
cadence and shifts a couple of LH notes down an octave in the second
section. Yet again it was the less distinctive version (Tomsic here)
that was chosen.

Sound on the "Hatto" disc seems "softened" compared to the originals,
both of which have a little more bite and detail, and this also helps
to make the performances less distinctive. In particular, Tomsic
(whose Scarlatti I like a lot-in the original) often uses accents and
subtle dynamic shadings to good effect, but these are somewhat
obscured in the Hatto-ized versions. As John Gavin pointed out in
another thread, the results are not really objectionable, but as
presented here, everything sounds a little more...homogenized.

I've tentatively identified the source for most of vol. 2: a
relatively obscure recording on a French label with a pianist who,
according to Google, has been mentioned in only four previous threads
on r.m.c.r! Details to follow when I can confirm them....

Seth Adelman