Well, this is certainly interesting and strange as hell.
Experiment.
1. Created a ProPhoto RGB tif file with a color gradient going from Lab 50,-50,0 to 50,-40,0 which is a moderately saturated darkish green. Saved as an RGB tif file and tagged with ProPhoto RGB. Contains no colors outside of that gradient.
2. Selecting optimize profile and using a profile with the standard 957 patch set for a 9500II I then added another 957 "Smart patches. The result was a new set of 957 patches with about 1/3 of them near neutrals.
3. I selected extract patches from an image then dragged and dropped the green gradient image into it. I1Profiler added the default 20 patches.
4. I then saved the chart image tif files, the pfx RGB patch file, and the I1Profiler CGATS patch file. Here's what the CGATs file had. Note the crazy "RGB" values in the last 20 locations.
CGATS.17
ORIGINATOR "i1Profiler - X-Rite, Inc."
INSTRUMENTATION "i1iSis XL ; Serial number 0"
DESCRIPTOR "9500 Baryta 957 D50 M2 ppRGB"
FILTER ""
KEYWORD "DEVCALSTD"
DEVCALSTD "XRGA"
CREATED "2020-09-27T18:40:11"
NUMBER_OF_FIELDS 5
BEGIN_DATA_FORMAT
SAMPLE_ID SAMPLE_NAME RGB_R RGB_G RGB_B
END_DATA_FORMAT
NUMBER_OF_SETS 977
BEGIN_DATA
1 - 18.69 255.00 255.00
2 - 0.00 221.91 249.46
3 - 19.33 181.39 255.00
4 - 5.33 112.18 247.76
......
973 - 46.83 -16.26 0.91
974 - 46.83 -16.26 0.91
975 - 46.83 -16.26 0.91
976 - 46.83 -16.26 0.91
977 - 46.83 -16.26 0.91
END_DATA
Yep, Those sure aren't RGB values. Looks like Lab values that their software created and added to a RGB CGATs file. Software bug.
So then I looked at the RGB values in the pxf file. Basically all entries at the end like this:
<cc:CreationDate>2020-09-28T02:39:46Z</cc:CreationDate>
<cc:DeviceColorValues>
<cc:ColorRGB ColorSpecification="Unknown">
<cc:R>81</cc:R>
<cc:G>125</cc:G>
<cc:B>91</cc:B>
</cc:ColorRGB>
</cc:DeviceColorValues>
</cc:Object>
<cc:Object ObjectType="Target" Name="Target968"
OK, that actually make sense. Sort of. At least they aren't Lab values with negative entries.
Next step, look at the green gradient tif file that was tagged ProPhoto RGB. The patches were RGB=(81,125,92). OK, the B value was 92 but we've already established that when I1Profiler saves pfx patches files it truncates fractional values while it rounds them when making a tif chart. Cool.
So now lets see what the tif file added patches are when the tif file is assigned the printer's profile. Ah, now that the patches are being interpreted in the printer's device colorspace guess what the Lab values as read out in Photoshop (Abs Col)?
Yep, Lab=47,-16,1
Gee, identical (after rounding) to Lab values erroneously added at the end the CGATs file.
All of which is FUBAR since adding a bunch of extra patches from an image which are printed at Lab 47,-16,1 don't do a darned thing to improve the printer's profile accuracy at Lab=50,-40,0 to 50,-50,0 which were supposedly the colors needing improvement.