Dekalog (1989)

According to the Criterion booklet, the audio for TVP's restorations of the episodes was sourced from "...35mm magnetic tracks and restored by the Criterion Collection using Pro Tools HD and iZotope RX."

The audio was, of course, already 'restored' by TVP, and any additional work done by Criterion would qualify as additional restoration.

But there are more important issues to discuss, unfortunately. Although both the TVP and Arrow blu-rays play at 25 fps, they are pitched ~0.7 semitones apart -- the Arrow disc higher and the TVP lower. 

The Criterion discs play ~0.7 semitones lower than the TVP (so ~1.4 lower than the Arrow).

And then there are the old Polish Warner DVDs, originally released in 2003:

The Warner DVDs are pitched identically to the TVP BDs. Here's a comparison for the opening notes (roughly 2.5 seconds) for episode 1 from each disc:

I have confirmed that the pitch discrepancy between the Arrow BDs and the TVP BDs/Warner DVDs holds true for at least the first four episodes. It's possible that after comparing the audio on the TVP masters to corresponding music cues on the soundtrack CD (Kompania Muzyczna Pomaton, cat. POM CD 018, 1992) Arrow found that the restored tracks completed by TVP were pitched incorrectly, and therefore chose to intervene. ...But my own preliminary comparisons to the CD indicate otherwise. (And I imagine that Arrow's team for this set, who have maintained a very transparent online presence, would have been forthright about having to do such a thing, no?)

So I propose that the Arrow blu-rays were mistakenly pitched ~4% (0.7 semitones) higher. I will be updating this post with more information after I finish my soundtrack comparisons.

Fidelity-wise, it's an easy win for the old Warner DVDs. Less high-frequency noise reduction, hissier but less veiled. One might suggest that the reduction in hiss on the TVP-restored tracks is the result of being an analogue generation closer to the first-generation mixes, but this isn't the case. There are instances in the restored tracks where specific sounds have been removed entirely (take, for instance, the rustling sound of Krzysztof's clothes as he does push-ups at the beginning of Episode 1 -- completely gone in the BDs, but present in the DVDs). The DVDs are extraordinarily detailed and exhibit none of the hallmarks of being sourced from inferior analogue elements.

The TVP and Arrow tracks are identical in terms of fidelity. Some additional NR and selective frequency attenuation were applied by Criterion to the further detriment of sonic detail on their blu-ray set.

Update:
Sample: Dekalog, Episode 4

Here's a video comparing a 20-second excerpt from the score of episode 4 between the Arrow blu-ray and the soundtrack CD. It makes the following comparisons:

Segment 1

•  ~20 seconds from the CD play first. It is an excerpt from track 7 and occurs specifically between 00:00:22.660 and 00:00:45.000.*

*Specifically from the 2012 Sony CD (Sony Music Poland, cat. 88697912412, released 2012 -- identical in pitch and tempo to Kompania Muzyczna Pomaton, cat. POM CD 018, released 1992). The track was folded to mono, resampled to 48 kHz, and had a -6 dB gain applied.  

• This is followed by the same ~20 seconds of the score excerpt taken from 00:10:02.350 to 00:10:24.220 on the Arrow blu-ray.

Segment 2

• The CD excerpt plays again, followed by the Arrow excerpt pitch-shifted 0.71 semitones lower.

Segment 3

• This is just the Arrow excerpt before and after the previous pitch adjustment. If you cannot detect any difference (equal to the effect of PAL speedup, without the tempo change), carry on enjoying your discs. If you can discern the difference, contact Arrow and complain or something.

Final update:
All ten episodes are affected. Arrow have not responded to my queries.